Peo v. Bannan

22CA0477 Peo v Bannan 03-26-2026

COLORADO COURT OF APPEALS

Court of Appeals No. 22CA0477
Boulder County District Court No. 19CR2042
Honorable Norma A. Sierra, Judge

The People of the State of Colorado,

Plaintiff-Appellee,

v.

Justin Lewis Bannan,

Defendant-Appellant.

JUDGMENT AFFIRMED

Division V
Opinion by JUDGE WELLING
Grove and Johnson, JJ., concur

NOT PUBLISHED PURSUANT TO C.A.R. 35(e)
Announced March 26, 2026

Philip J. Weiser, Attorney General, Grant R. Fevurly, Senior Assistant Attorney
General, Denver, Colorado, for Plaintiff-Appellee

The Noble Law Firm, LLC, Antony Noble, Jennifer Tuttle, Lakewood, Colorado,
for Defendant-Appellant
¶1 Justin Lewis Bannan appeals the judgment of conviction

entered after a jury found him guilty of four felonies. We affirm.

I. Background

¶2 On October 16, 2019, A.M., an acupuncturist, arrived at her

office. As she opened her office door, Bannan, who was sitting in

the corner of her office, shot her in the arm. Bannan was a co-

owner of the building where A.M. worked. Police arrived and

arrested Bannan without incident. A.M. told police that after

Bannan shot her, he said to her, “I’m sorry, the Russian mafia is

after me.”

¶3 Bannan was charged with two counts of attempted first degree

murder, two counts of first degree assault, possession of a weapon

on school grounds,1 and four crime of violence sentence

enhancement counts. Bannan pleaded not guilty by reason of

insanity (NGRI). His case proceeded to a jury trial on August 30,

2021.

1 This charge appears to be based on an allegation that Bannan

possessed a firearm on the University of Colorado campus, which is
near A.M.’s office. This charge, however, was voluntarily dismissed
by the People prior to trial, so there is limited information about it
in the record.

1
¶4 At trial, Bannan’s defense was that he was unable to form the

requisite mental state for the charges under both an insanity and

involuntary intoxication theory. Bannan played defensive tackle for

several teams in the National Football League (NFL), and with

respect to NGRI, he claimed that multiple concussions that he

sustained during his football career negatively affected his brain

and prevented him from forming the requisite mental state. As for

involuntary intoxication, Bannan argued that he was overprescribed

Adderall, which also negatively affected his brain. The People

argued that Bannan was able to form the requisite mental state at

the time of the offense. Both sides presented multiple experts and

lay witnesses related to these issues.

¶5 The jury convicted Bannan of attempted first degree murder

(extreme indifference); first degree assault (deadly weapon); first

degree assault (extreme indifference); and the lesser included

offense of attempted second degree murder. After merging some of

the counts, the trial court sentenced Bannan to two concurrent

sentences of sixteen years in the custody of the Department of

Corrections.

2
II. Analysis

¶6 Bannan contends that the trial court erred by (1) limiting the

scope of his expert witnesses’ testimony; (2) limiting the scope of his

lay witnesses’ testimony; (3) limiting his cross-examination of the

prosecution’s expert witnesses; (4) allowing the prosecution to elicit

irrelevant testimony on cross-examination from his expert witness;

and (5) denying his request to call an expert witness in surrebuttal.

Bannan also contends that cumulative error warrants reversal. We

address, and reject, each contention in turn below.

A. Standard of Review

¶7 We review a trial court’s evidentiary decisions for an abuse of

discretion. People v. Murphy, 2021 CO 22, ¶ 16. A trial court

abuses its discretion when its decision was “manifestly arbitrary,

unreasonable, or unfair, or based on a misunderstanding or

misapplication of the law.” People v. Heredia-Cobos, 2017 COA 130,

¶ 6.

B. Scope of Expert Testimony

¶8 First, Bannan argues that the trial court erred by restricting

his experts’ testimony to the contents of their reports. The People

respond that the law requires such a limitation, otherwise criminal

3
defendants would be allowed to ambush the People with unexpected

arguments at trial. We conclude that, even if the court abused its

discretion by imposing this limitation, it didn’t reversibly err.

1. Additional Facts

¶9 At his arraignment, Bannan entered an NGRI plea. He

asserted that he suffered from chronic traumatic encephalopathy

(CTE)2 or other brain trauma that constituted a mental disease or

defect. As required by statute, the trial court ordered him to

undergo a sanity evaluation, which he did.

¶ 10 As part of his pretrial disclosures and as required by section

16-8-103.6(2)(a), C.R.S. 2025, Bannan disclosed to the People the

names and addresses of twelve treatment providers. Soon after,

Bannan supplemented this disclosure with two more names and

addresses of treatment providers. The trial court then ordered that

Bannan supplement this information with the providers’ telephone

numbers, the approximate dates of treatment, a general description

of the service each provided, and any diagnosis. Then, pursuant to

2 CTE is a brain disease linked to repeated trauma to the head. See
Mayo Clinic, Chronic traumatic encephalopathy,
https://perma.cc/SQT8-4RFN.

4
Crim. P. 16, Bannan disclosed seven expert witnesses. From our

review of the record, there isn’t any indication that Bannan failed to

comply with his statutory obligation to provide the People with

reports from these seven expert witnesses.

¶ 11 The People then filed a motion in limine to exclude any

evidence relating to CTE on the grounds that no treatment provider

had diagnosed Bannan as having such disease or disorder. The

trial court addressed this motion at a pretrial hearing. At the

hearing, the parties discussed whether Bannan would be seeking to

introduce evidence related to CTE. The parties clarified that doctors

can’t diagnose anyone with CTE until an autopsy is performed after

the patient’s death. But defense counsel explained that their

experts would opine that, based on Bannan’s behavior, conduct,

and head trauma history, they expect that after Bannan’s death he

would be diagnosed as having suffered from CTE during his

lifetime.

¶ 12 The People objected, arguing that this testimony wouldn’t be

relevant because it didn’t include a nexus between Bannan’s brain

trauma, including CTE, and his ability to form the requisite mental

state for the charged conduct. Defense counsel responded that this

5
connection wasn’t “something [the experts] would be able to opine

to because that [was] a question for the jury based on the evidence

presented.” But ultimately, defense counsel represented that they

believed that the expert testimony, when taken as a whole, would

show that CTE prevented Bannan from forming the requisite mental

state for the charged conduct.

¶ 13 The trial court allowed the defense to file a written response to

the People’s motion in limine and didn’t address the issue again

until the morning of the first day of trial. That morning, the trial

court explained that “[t]o the extent that the [c]ourt finds there

is . . . an expert whose expertise permits that witness to render an

expert opinion that [Bannan] presented consistent with other

individuals who have later been diagnosed with CTE, the [c]ourt

may be in a position of permitting that testimony.” Defense counsel

then clarified that the experts could testify that “to a reasonable

degree of medical probability” that Bannan suffers from CTE. The

trial court asked whether a report contained such an opinion and

ruled that if there wasn’t a report that did, then any testimony to

that regard wouldn’t be allowed.

6
¶ 14 The trial court revisited this matter and ruled on what each

expert could testify to at trial. It repeated its earlier ruling that the

experts would be limited to testifying to matters only in their

reports. But it clarified that it would allow Dr. Marc Treihaft, one of

the defense experts, to testify about his impression that Bannan’s

symptoms may be a result of multiple concussions and CTE.

Defense counsel then reiterated their position that the connection

between the required mens rea and CTE, which the People still

asserted was lacking, was a question for the jury.

¶ 15 Later in the trial, Bannan called two of these experts —

Dr. John Hughes and Dr. Gregory Hipskind. The People objected to

parts of Dr. Hughes’s testimony on the basis that it was beyond the

scope of his report, and the trial court sustained those objections.

As Bannan argues on appeal, this testimony included the following:

• Defense counsel asked, “And what happens to the brain

internally when somebody has one of these external

concussive —” Dr. Hughes answered, “According to the

famous neurologist Robert Cantu, the brain goes into a —”

The prosecutor interrupted him, objecting that the

7
testimony was “beyond the scope of the opinion that was

discovered in this particular case.”

• Dr. Hughes testified about his opinion that Bannan suffered

from a traumatic brain injury. During that testimony, he

began speaking about Bannan’s computed tomography

angiogram that showed microvascular defects. The

prosecutor objected, explaining that “[n]o such document

has been provided in discovery” and “[n]or is it cited in . . .

the expert’s report.”

• Defense counsel asked, “And how long can symptoms from

one concussion affect somebody?” Dr. Hughes responded,

“A lifetime.” The prosecutor objected that this was “beyond

the scope of the report provided by this expert.” The trial

court sustained the objection and asked the jurors to

disregard the answer.

• Defense counsel asked, “Dr. Hughes, in [Bannan’s] case, the

traumatic brain injury, was it caused from one

concussion?” The prosecutor objected that this was

“beyond the scope of the material provided by this expert.”

8
• Defense counsel asked, “People with executive function

limitations, would you expect to see them running late

because of the decision-making aspect?” Dr. Hughes

responded, “[y]es.” The prosecutor objected that this was

“beyond the scope of this expert’s opinion.” The trial court

sustained the objection and asked the jury to disregard the

response.

• Defense counsel asked if Dr. Hughes’s opinion would

change if Bannan had been taking Adderall. Dr. Hughes

responded that “[i]f [Bannan] had been taking excessive

amounts of Adderall, that could have potentially pushed

him over the edge. I have had patients with traumatic brain

injury have seizures due to —” The prosecutor interrupted,

objecting that this was “well beyond the scope of this

witness’s provided report.”

¶ 16 Finally, during the testimony of another defense expert,

Dr. Karen Fukutaki, the trial court sustained an objection that her

testimony regarding when Bannan had brain surgery to place a

shunt in his brain was beyond the scope of the records she

reviewed.

9
2. Analysis

¶ 17 We address whether the trial court reversibly erred when it

limited defense experts to testifying about matters contained in

their reports. We conclude that it didn’t.

a. Standard of Reversal

¶ 18 We first discuss the proper standard of reversal. Bannan

contends that we should review his contentions for constitutional

error because the court’s rulings deprived him of a meaningful

opportunity to present a complete defense. People v. Cline, 2022

COA 135, ¶ 70. But such a deprivation only occurs “where the

defendant was denied virtually his only means of effectively testing

significant prosecution evidence.” People v. Conyac, 2014 COA 8M,

¶ 93. That isn’t the case here. The trial court’s ruling that the

defense experts could testify to only what was in their reports didn’t

virtually deny him of his only means of responding to the People’s

case. In fact, the experts were still able to testify to a wide variety of

opinions. See Cline, ¶ 79 (explaining that the defendant “had ample

opportunity to present evidence” through cross-examination of the

prosecution’s witnesses and direct examination of his witnesses).

10
¶ 19 Also, Bannan presented evidence during trial to support his

theory of defense. His defense included testimony from two experts

who testified that Bannan suffered from a traumatic brain injury

and to the effects of such an injury, as well as that he was

prescribed about one hundred and fifty percent of the maximum

recommended dose of Adderall.

¶ 20 The defense also called witnesses to testify about Bannan’s

history of concussions. One of his ex-teammates testified that he

witnessed Bannan sustain many head injuries while playing

football. And an expert opined that Bannan suffered from

“hundreds to thousands of concussions” in his career. Upon our

review of the record, Bannan was permitted to present evidence

about his mental state, including the effect of multiple concussive

events and a traumatic brain injury. Therefore, Bannan was still

able to present a defense and rebut the People’s evidence. See

People v. Lanari, 926 P.2d 116, 122 (Colo. App. 1996) (concluding

that a defendant wasn’t denied his constitutional right to present a

defense when defense witnesses testified to his state of mind before

and after the offense).

11
¶ 21 In sum, because the trial court’s ruling still permitted the

experts to testify to what was in their reports, including testimony

about his mental state, we can’t say that it barred Bannan from

subjecting the prosecution’s case to “meaningful adversarial

testing.” Krutsinger v. People, 219 P.3d 1054, 1061 (Colo. 2009).

Therefore, the non-constitutional harmless error applies. Under

that standard, “reversal is required only if the error affects the

substantial rights of the parties.” Hagos v. People, 2012 CO 63,

¶ 12. Meaning, “we reverse if the error ‘substantially influenced the

verdict or affected the fairness of the trial proceedings.’” Id.

(citation omitted).

b. Any Error was Harmless

¶ 22 Now, applying that standard, and assuming that the trial

court abused its discretion in ordering Bannan’s expert witnesses to

testify to only matters in their reports, we conclude that any error

was harmless, as defense counsel didn’t make an adequate offer of

proof — either to the trial court or us on appeal — as to what the

experts would have testified to that was outside of their reports had

they been permitted to do so and why that proffered testimony

would have been materially helpful to Bannan’s theory of defense.

12
See People v. Drake, 748 P.2d 1237, 1245-46 (Colo. 1988)

(concluding that any error by the trial court in sustaining the

prosecution’s objections to certain portions of a defense expert’s

testimony wasn’t sufficiently prejudicial to warrant reversal because

“the defendant did not make an offer of proof to the trial court to

establish for the record precisely what [the expert] would have said,

had he been permitted to testify”); People v. Hise, 738 P.2d 13, 16

(Colo. App. 1986) (explaining that failure to give a sufficient offer of

proof left the reviewing court unable to determine in what way the

exclusion of evidence was prejudicial and so any error was

harmless). We reach this conclusion because we can’t discern from

the record that the defense was seeking to offer any evidence

establishing a link between CTE and the ability to form criminal

intent.

¶ 23 Defense counsel did represent to the trial court that some of

their experts, if permitted to, could testify to a reasonable degree of

medical probability that Bannan suffers from CTE. But this offer of

proof is missing any link to how suffering from CTE likely affected

Bannan’s ability to formulate the requisite mental state for the

crimes charged. Defense counsel only vaguely mentioned that,

13
when considered in the aggregate, the sum of the defense experts’

testimony might show this connection. But when the trial court

directly asked defense counsel whether their witnesses could testify

that Bannan’s likely CTE prevented him from formulating the

requisite mental state, defense counsel said no and explained that

was an ultimate conclusion that was left for the jury.

Notwithstanding this, the record doesn’t reveal the details of what

each expert would have said beyond what was already in their

reports. And without this link, we can’t conclude that Bannan was

prejudiced by any error in excluding testimony about whether he

likely suffers from CTE.

¶ 24 The trial court recognized that testimony about the nexus

between CTE and Bannan’s ability to form the requisite mental

state was likely admissible. The court said that to the extent it

found that there was an “expert whose expertise permits that

witness to render an expert opinion that [Bannan] presented

consistent with other individuals who have later been diagnosed

with CTE, the [c]ourt may be in a position of permitting that

testimony.” Therefore, it’s unclear if the trial court even would have

sustained an objection by the prosecutor that such testimony was

14
outside the expert’s report had the defense sought to have their

experts testify to this.

¶ 25 Also, Bannan’s experts were still permitted to testify to the

opinions contained in their report, which included Dr. Hughes’s

opinion that Bannan suffered from a traumatic brain injury,

Dr. Hipskind’s opinion that Bannan had a “classic traumatic brain

injury pattern”, and Dr. Fukutaki’s opinion that Bannan was

prescribed about one hundred and fifty percent of the maximum

recommended dose of Adderall. All this testimony supported his

theory of defense. See Drake, 748 P.2d at 1246 (recognizing that, in

analyzing whether a defendant was sufficiently prejudiced by

excluded portions of his expert’s testimony, that the jury was still

informed of the expert’s opinion).

¶ 26 Simply put, without a sufficient offer of proof, we can’t

conclude that the excluded testimony about whether Bannan

suffered from CTE prejudiced him. See Lanari v. People, 827 P.2d

495, 503 (Colo. 1992) (“An offer of proof also serves the important

purpose of establishing a basis in the record for appellate review of

the trial court’s ultimate ruling.”). And when we look at the

testimony Bannan asserts was improperly excluded on appeal, none

15
of it addresses this missing nexus. Similarly, since we don’t have

an offer of proof as to what the answers would have been to the

seven questions to which objections were sustained, we can’t say

the court’s ruling on these objections prejudiced Bannan. See

Rhodig v. Cummings, 418 P.2d 521, 502 (Colo. 1966) (concluding

there was no reversible error when the trial court precluded defense

experts from testifying to certain matters because “the defendant

failed to make an offer of proof to show to the trial court or this

[c]ourt what the testimony of the doctors” would have been); cf.

People v. Sandoval, 805 P. 2d 1126, 1128 (Colo. App. 1990)

(concluding that the trial court erred in excluding evidence and

such exclusion wasn’t harmless because “defense counsel made an

offer of proof” that “defendant’s abnormal behavior [was] caused by

his underlying, psychological condition” (emphasis added)).

¶ 27 Accordingly, we conclude that any error by the trial court in

limiting the defense experts’ testimony to their reports was

harmless.

C. Scope of Lay Witness Testimony

¶ 28 Second, Bannan contends that the trial court erred when it

ruled that one of his lay witnesses, Mitchell Unrein, couldn’t testify

16
that Bannan’s “brain was sick” because such testimony was an

expert opinion. He also contends that the trial court erred when it

sustained the People’s objection to testimony from Unrein and Beau

Williams (a lay witness called by the People) about their personal

experiences with concussions on relevance grounds. We disagree

with both contentions.

1. Additional Facts

¶ 29 Both Unrein and Williams are former NFL players. On the first

day of trial, defense counsel explained to the trial court that he

intended to call lay witnesses to opine that Bannan’s “brain was

sick” and that Bannan “didn’t seem normal” to them. The trial

court explained that it would sustain an objection to the former

statement because it was “in the way of a diagnosis.”

¶ 30 Then during trial, the trial court sustained the People’s

objections to the lay witnesses testifying about their own personal

experience with brain trauma due to playing football. Unrein

testified that “[b]ut, for me, I’m like — I was going through the same

thing. So, like, when he was going through all that, I mean, I —

your mind starts playing tricks on you. It’s — you can’t control

what your thoughts are.” The People objected that this was

17
improper expert testimony. After a discussion at the bench, the

trial court ruled that if Unrein was referring to his own mind, such

testimony was irrelevant. The trial court also sustained the

People’s relevance objection as to Williams’s testimony about his

own personal experience of being knocked out while playing

football.

2. Applicable Law

¶ 31 CRE 701 provides that

If the witness is not testifying as an expert, the
witness’ testimony in the form of opinions or
inferences is limited to those opinions or
inferences which are (a) rationally based on the
perception of the witness, (b) helpful to a clear
understanding of the witness’ testimony or the
determination of a fact in issue, and (c) not
based on scientific, technical, or other
specialized knowledge within the scope of Rule
702.

¶ 32 And section 16-8-109, C.R.S. 2025, provides that

In any trial or hearing in which the defendant’s
mental condition is an issue, a witness not
specially trained in psychiatry or psychology
may testify as to the witness’s observation of
the defendant’s actions and conduct, and as to
conversations that the witness has had with
the defendant bearing upon the defendant’s
mental condition, and the witness must be
permitted to give opinions or conclusions
concerning the defendant’s mental condition.

18
¶ 33 In interpreting this statute, the Colorado Supreme Court has

explained that it doesn’t “allow[] a lay witness to opine as to a

defendant’s specific diagnosis.” Dunlap v. People, 173 P.3d 1054,

1098 (Colo. 2007).

¶ 34 Further, evidence must be relevant to be admissible. CRE

402. Relevant evidence is “evidence having any tendency to make

the existence of any fact that is of consequence to the determination

of the action more probable or less probable than it would be

without the evidence.” CRE 401.

3. Analysis

¶ 35 First, the trial court didn’t abuse its discretion by precluding

Unrein from testifying that Bannan’s “brain was sick” pursuant to

CRE 702, as such testimony can be reasonably characterized as

offering a diagnosis. See Dunlap, 173 P.3d at 1098. In reaching its

conclusion that the precluded testimony was inadmissible, the

court distinguished it from Unrein’s permissible lay opinion that

Bannan “didn’t seem normal” to him. We can’t say that the trial

court abused its discretion in drawing the line that it did.

¶ 36 Second, Bannan argues that the trial court erred in sustaining

the People’s objections on relevance grounds to witnesses testifying

19
to their own personal experiences with brain trauma. He contends

that the testimony was proper under CRE 701 and section 16-8-

109. Specifically, he argues that the statute allows lay opinions

based on personal experience, and that the excluded testimony was

proper because it helped lay the foundation for witnesses’ lay

opinions as to Bannan’s mental state. We aren’t persuaded.

¶ 37 While section 16-8-109 allows a lay witness to testify as to

their personal experience with the defendant’s mental condition, it

doesn’t permit the witness to testify regarding their own personal

experience generally. See § 16-8-109 (explaining that a lay witness

“may testify as to the witness’s observation of the defendant’s

actions and conduct” (emphasis added)).

¶ 38 Moreover, the two foundational requirements “which must be

met before a lay witness can express his opinion as to the sanity of

another” are “(1) it must be shown that the lay witness had an

adequate means of becoming acquainted with the person whose

sanity is in issue, and (2) the contacts must be proximate in time to

the alleged offense.” People v. Medina, 521 P.2d 1257, 1259 (Colo.

1974). A witness’s personal experience with head trauma doesn’t

help establish either of these foundational requirements. And the

20
People don’t dispute that Bannan laid the proper foundation for

both Unrein and Williams to testify about Bannan’s mental status.

But we reject Bannan’s contention that the witnesses’ testimony

about their own experience with head trauma was proper

foundational testimony. Bannan also hasn’t explained why this

testimony tended to make a fact of consequence more or less

probable. CRE 401. Accordingly, we conclude that the trial court

didn’t abuse its discretion by limiting the scope of lay witness

testimony as it did at trial.

D. Scope of Cross-Examination of Prosecution Witnesses

¶ 39 Next, Bannan argues that the trial court erred by sustaining

the People’s beyond the scope and relevancy objections during

Bannan’s cross-examination of three prosecution witnesses. We

discern no abuse of discretion.

1. Beyond the Scope of Direct Examination

¶ 40 CRE 611(b) provides that cross-examination “should be limited

to the subject matter of the direct examination and matters

affecting the credibility of the witness” but that “[t]he court may, in

the exercise of [its] discretion, permit inquiry into additional matters

as if on direct examination.” The beyond the scope objections that

21
Bannon challenges on appeal came during the testimony of

Dr. John Geraghty, who was Bannan’s team doctor when he played

for the Broncos and continued treating Bannan after Bannan

stopped playing football.

¶ 41 Dr. Geraghty’s testimony on direct examination focused on his

treatment of Bannan for attention deficit disorder (ADD), including

Bannan’s ADD symptoms, Dr. Geraghty prescribing Bannan

Adderall, Bannan’s request to refill that prescription, his

conversations with Bannan about the risks and dangers of Adderall,

the amount of Adderall he prescribed for Bannan, and his

subsequent decision to switch Bannan’s prescription from Adderall

to Provigil. The People also asked Dr. Geraghty two questions about

concussions — one, if he recalled treating Bannan for a concussion

in March 2019 (he said he didn’t); and two, if he recalled whether

Bannan had any concussions after his NFL career (he wasn’t aware

of any). In sum, Dr. Geraghty’s direct testimony centered on him

prescribing Bannan Adderall.

¶ 42 As relevant here, the People objected five times during defense

counsel’s cross-examination of Dr. Geraghty. The trial court

sustained all five of the objections, ruling that the questions were

22
beyond the scope of the direct examination. Those questions were

as follows:

(1) “So you’re aware that [Bannan] had brain surgery in

October 2020?”

(2) “And, Dr. Geraghty, have you reviewed the records from

Mr. Bannan’s other physicians?”

(3) “Have you ever reviewed a SPECT scan done of Mr.

Bannan?”

(4) “Have you reviewed a report in this case drafted — or

written by Dr. Fukutaki?”

(5) “Were you aware of Mr. Bannan having brain trauma?”

¶ 43 Also during Dr. Geraghty’s testimony, defense counsel asked

him a sixth question that is pertinent to the appeal,

(6) “And when you met with Mr. Bannan, the first time you

met with him for a physical after the . . . October 16th,

2019, shooting incident, did you discuss any other

concerns that he had, medically speaking, in ongoing

treatment?”

¶ 44 The People objected that this question was beyond the scope of

direct examination, and the trial court told defense counsel to

23
narrow the question “as to the discontinuation of the Adderall.”

Defense counsel then asked, “Doctor, this is when you discontinued

Mr. Bannan’s Adderall, right?”

¶ 45 Bannan argues that defense counsel asked all six of these

questions to impeach Dr. Geraghty’s credibility, so the court abused

its discretion in sustaining the objection as beyond the scope of

direct examination. We aren’t persuaded that the court abused its

discretion.

¶ 46 Again, Dr. Geraghty’s testimony on direct centered on

prescribing Bannan Adderall, which started around 2013, and the

symptoms Bannan was experiencing related to ADD. At no point

did the People ask Dr. Geraghty about reports or recommendations

from other health care providers. Therefore, defense counsel’s

questions on cross-examination weren’t “germane to the direct

examination” and didn’t “qualify[] or destroy[] it, or tend[] to

elucidate, modify, explain, contradict, or rebut testimony.” People

v. Sallis, 857 P.2d 572, 574 (Colo. App. 1993). Dr. Geraghty only

testified on direct as to his opinions and treatment of Bannan for

ADD.

24
¶ 47 And we aren’t persuaded that defense counsel’s questions

relating to other doctors went to Dr. Geraghty’s credibility and thus

should have been allowed. Bannan has failed to explain why

Dr. Geraghty’s review, or failure to review, other doctors’ reports or

recommendations would impugn his credibility. Dr. Geraghty

prescribed Bannan Adderall, and we fail to see how his alleged

failure to review all of Bannan’s other medical records would have

undermined his testimony about Bannan’s Adderall prescription

and symptoms. And even if such questions implicated

Dr. Geraghty’s credibility, the trial court could have reasonably

found that the danger of confusing the jury — because it implicated

issues not related to Dr. Geraghty — outweighed any probative

value to his credibility. Therefore, the trial court didn’t abuse its

discretion in sustaining the People’s objection to defense counsel’s

questions to Dr. Geraghty about Bannan’s other doctors’ reports

and recommendations. See People v. Marin, 686 P.2d 1351, 1353

(Colo. App. 1983) (“The right of cross-examination extends only to

areas encompassed in direct examination, and anything outside of

direct examination is completely discretionary with the court.”).

25
¶ 48 The trial court also didn’t abuse its discretion by sustaining

the People’s objections to defense counsel’s questions about

Bannan’s brain trauma for being beyond the scope of direct

examination. Again, the People didn’t ask Dr. Geraghty about these

topics on direct examination, so it was within the trial court’s

discretion to not allow defense counsel to ask Dr. Geraghty about

them on cross-examination.

¶ 49 In fact, Dr. Geraghty testified on cross-examination that

additional knowledge about Bannan’s history of brain trauma

wouldn’t have impacted his decision to prescribe Adderall for his

ADD. The trial court allowed the following exchange between

defense counsel and Dr. Geraghty on cross-examination right before

the fifth question:

[DEFENSE COUNSEL]: And you would
be . . . concerned about somebody taking
Adderall with concussions; isn’t that right?

[DR. GERAGHTY]: Actually, through other
doctors that I have interacted with who have
dealt with brain traumas, it’s not an unusual
medication to use.

26
¶ 50 This testimony established that any trauma to Bannan’s brain

wouldn’t have been a concern for Dr. Geraghty when he was

deciding whether to prescribe Adderall to Bannan.

¶ 51 And the People’s two questions on direct examination about

concussions don’t change this analysis. These specific questions

about Bannan’s concussion history didn’t open the door for defense

counsel to ask Dr. Geraghty more generally about brain trauma and

Bannan’s other doctors’ opinions on cross-examination because

they focused on Dr. Geraghty’s own knowledge of Bannan’s

concussion history, of which he had none. Accordingly, we discern

no error in any of the trial court’s rulings regarding these six

questions.

2. Relevance

¶ 52 Bannan challenges the court’s ruling sustaining three

relevance objections raised by the People. We address each

question, in turn, below.

¶ 53 The first question was to Dr. James Kelly, the People’s expert

witness in neurology and traumatic brain injury. Right before the

question challenged on appeal, Dr. Kelly had testified that Bannan

had some limitation in moving his neck. Defense counsel then

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asked, “And what was the limitation? He couldn’t turn his head all

the way around?” The trial court sustained the People’s objection to

this question on relevance grounds.

¶ 54 Bannan argues that the details of his neck injury were

relevant because they would have supported an inference that his

brain injury was more severe than one unaccompanied by a neck

injury. But Bannan doesn’t explain why whether he had limited

ability to turn his neck to the side as opposed to a limited ability to

bend it up and down makes it more or less likely that he suffered a

severe brain injury. See People v. Moore, 2021 CO 26, ¶ 33

(“[E]vidence that is ‘relevant to the issue of insanity’ is evidence that

tends to prove or disprove the issue of insanity — that is, evidence

that is probative of what is defined as insanity.” (quoting § 16-8-

107(3)(a), C.R.S. 2025)). So, we discern no abuse of discretion in

the trial court’s relevancy ruling.

¶ 55 The second question was to Dr. Charles Harrison, who

conducted Bannan’s first sanity evaluation. The People asked him,

“Did [Bannan] express to you any additional treatment that he had

other than [lumbar punctures, barometric treatments, oxygen

chambers, and stem cell treatments] or had planned to have?”

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¶ 56 Bannan argues that understanding the treatment he had or

planned to undergo after the shooting was relevant to his claim that

he had a mental condition that prevented him from forming the

required mens rea. But, again, Bannan doesn’t explain why other

treatments, especially any planned for the future, would have

impacted his ability to form the requisite mens rea at the time of the

offense. Without that connection, we discern no abuse of discretion

in the trial court’s refusal to permit defense counsel to ask this

question.

¶ 57 The third question was to Dr. Geraghty. After previously

prescribing Adderall to treat Bannan’s ADD, Dr. Geraghty changed

the prescription to Provigil. After confirming with Dr. Geraghty that

a patient could get “no refills” on a single Adderall prescription,

defense counsel asked, “[I]n 2019, Provigil had . . . only three refills

[that] could be allowed . . .?”

¶ 58 Bannan argues that because more refills are allowed for

Provigil than for Adderall, that means Provigil isn’t as highly

regulated as Adderall, indicating that there are greater risks

associated with taking Adderall. Therefore, he argues, this question

was relevant to his defense that he was involuntary intoxicated due

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to his high Adderall prescription. Bannan asks us to infer that

because Adderall is more regulated than Provigil, there are more

risks to taking Adderall. But he hasn’t provided evidence of this

inference, and without that, we discern no abuse of discretion by

the trial court in excluding this testimony on relevancy grounds.

¶ 59 Accordingly, the trial court didn’t abuse its discretion in

sustaining relevance objections to these three questions.

E. Scope of Cross-Examination of Defense Witness

¶ 60 Bannan next argues that the trial court abused its discretion

by allowing the People to elicit irrelevant testimony from

Dr. Fukutaki, a defense expert witness. Again, we disagree.

1. Additional Facts

¶ 61 After pleading NGRI, Bannan underwent his first sanity

evaluation per the trial court’s order. The evaluating doctor opined

that Bannan was sane at the time of the offense. After that

evaluation was completed, Bannan requested that the trial court

order a second sanity evaluation to be completed by a different

evaluator, Dr. Fukutaki, pursuant to section 16-8-108(1)(a), C.R.S.

2025. The trial court granted his request, explaining that an

independent order for an evaluation would issue and that the

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interview must be video and audio recorded, as required by statute.

See § 16-8-108(1)(a). But due to an administrative error by the

court, the order issued was for a second competency evaluation, not

for a sanity evaluation. Competency evaluations aren’t required to

be recorded. See § 16-8.5-102 to -103, C.R.S. 2025.

¶ 62 A couple of weeks later, Bannan filed a motion to clarify this

order. In response, the trial court set aside the mistaken

competency order and issued a new order for a second sanity

evaluation to be completed by Dr. Fukutaki. But before the

corrected order issued, Dr. Fukutaki completed her evaluation of

Bannan. Thus, at the time of her evaluation, the only order she

had from the court was for a competency evaluation. Dr. Fukutaki

didn’t audio or video record the interview.

¶ 63 Bannan called Dr. Fukutaki to testify as an expert at trial.

Before her testimony, Bannan asked that the trial court exclude as

irrelevant any testimony or questioning regarding her evaluation

not being recorded pursuant to section 16-8-108(1)(a). The People

explained that they intended to ask questions on the matter

because Dr. Fukutaki’s decision to not record the evaluation went

“directly to her bias and motive, and any assertion that

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Dr. Fukutaki was unaware that a sanity evaluation had been

ordered in this case lacks credence based on the fact that she took

the unusual step, in a competency evaluation, to address the issue

of insanity.” Indeed, after opining that Bannan was competent to

proceed, Dr. Fukutaki wrote that Bannan “denied guilt for the

charges he faces. He reported his gun accidentally discharged,

leading to the injury [A.M.] suffered. Therefore, offering an opinion

regarding sanity appears unethical.” The trial court ruled that it

might permit the People’s questions if it determined that they bore

on Dr. Fukutaki’s credibility or bias.

¶ 64 As relevant here, the trial court overruled Bannan’s objections

to the People’s cross-examination of Dr. Fukutaki on three

occasions. The questions by the People were as follows:

• “Doctor, are you aware that the Court in this case issued an

order on November 20th, 2020, authorizing you to conduct

a sanity evaluation in this case at the request of [defense

counsel]?”

• “You would agree, Doctor, that the statute requires sanity

evaluations be recorded?”

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• “And you would agree, Doctor, that when we’re talking

about a competency evaluation, as it’s authorized by

statute, that a competency evaluation as authorized by

statute does not address issues of sanity?”

2. Applicable Law

¶ 65 “[T]he partiality of a witness is always relevant.” Margerum v.

People, 2019 CO 100, ¶ 10. Indeed, “when a witness testifies

against a party, the party has a right to impeach that witness’s

credibility.” Id. at ¶ 11. “Any witness’s credibility can be attacked

by unearthing any potential source of impartiality, such as bias or

an ulterior motive.” Id. at ¶ 10. But a trial court must exercise its

discretion to preclude inquiries that “have little effect on the

witness’ credibility but would substantially impugn [their] moral

character.” People v. Taylor, 545 P.2d 703, 705 (Colo. 1976).

3. Analysis

¶ 66 Bannan argues that the trial court erred in overruling his

objections to three of the People’s questions of Dr. Fukutaki on

cross-examination. Specifically, he argues that the testimony was

irrelevant, not probative of her credibility, and misleadingly

impugned her character. We disagree with each contention.

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¶ 67 The trial court didn’t abuse its discretion in concluding that

the three questions identified above were relevant to Dr. Fukutaki’s

credibility as a defense expert witness. The timing of events is

critical to reaching this conclusion. Although the court issued the

corrected order for a sanity evaluation after Dr. Fukutaki completed

the competency evaluation, it did so before she completed her

report. And it’s certainly a reasonable area of inquiry as to why

Dr. Fukutaki opted not to perform a statutorily compliant sanity

evaluation after receiving the corrected order. In other words, it

was the People’s proposition that Dr. Fukutaki could have redone

the evaluation as a sanity evaluation pursuant to the new order.

Therefore, we can’t conclude that it was an abuse of discretion for

the trial court to permit the People to inquire into Dr. Fukutaki’s

reasoning for not recording the evaluation or even re-doing the

evaluation pursuant to the new order. Indeed, Bannan had filed

the motion to clarify (explaining that the court’s order should have

been for a sanity evaluation) three days before Dr. Fukutaki

completed her evaluation. And Dr. Fukutaki didn’t file her written

report with the court until almost four months after the court

issued the corrected order. Therefore, the trial court didn’t abuse

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its discretion in overruling Bannan’s objections because the

circumstances suggested that Dr. Fukutaki could have known that

the competency order was a mistake and that she should have been

conducting a sanity evaluation. See Ross v. Colo. Nat’l Bank of

Denv., 463 P.2d 882, 887 (Colo. 1969) (“[O]nce a witness testifies as

an expert, he subjects himself to the most rigid kind of cross-

examination . . . .”); see also People v. Houser, 2013 COA 11, ¶ 58

(“[C]ourts have wide latitude to reasonably limit cross-

examination . . . .”). So, the People could inquire into these

circumstances.

¶ 68 Furthermore, these questions didn’t cross the line from

impeaching her credibility to impugning her character. Again, these

questions related to court orders and an evaluation for the pending

case. Cf. People v. Cole, 654 P.2d 830, 833-34 (Colo. 1982)

(explaining that questions about “unrelated arrests and citizen

complaints of the use of excessive force” of a police officer was a

“direct attack upon the general character of the witness”).

Dr. Fukutaki could have had a reasonable explanation for why she

didn’t record the evaluation or why she didn’t conduct a new sanity

35
evaluation. Nothing about this line of inquiry impugned her

character.

¶ 69 Accordingly, we discern no error by the trial court in

overruling Bannan’s relevance objections to the People’s cross-

examination of Dr. Fukutaki.

F. Surrebuttal Expert Witness

¶ 70 Fifth, Bannan argues that the trial court erred by denying his

request to call an expert witness, Dr. Kevin Lillehei, in surrebuttal.

We disagree.

1. Additional Facts

¶ 71 Both Bannan and the People endorsed Dr. Lillehei as an

expert witness but neither side ended up calling him to testify in

their case-in-chief. The People presented twelve witnesses in their

rebuttal case, none of whom were Dr. Lillehei. After the People’s

presentation of their rebuttal case, Bannan requested that he be

allowed to call Dr. Lillehei as a surrebuttal expert witness.

¶ 72 After hearing argument from both sides on this request, the

trial court explained that it “agree[d] [with the People] that it is

appropriate to consider surrebuttal only in instances where there is

presentation in the rebuttal case of evidence that then permits a

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surrebuttal case, which in the [c]ourt’s opinion in this instance,

there was not.” The trial court then denied Bannan’s request to call

Dr. Lillehei in surrebuttal.

2. Applicable Law

¶ 73 “A decision whether to allow surrebuttal generally lies within

the discretion of the trial court.” People v. Brockman, 699 P.2d

1339, 1342 (Colo. 1985). But “trial courts should permit

defendants to introduce evidence on surrebuttal that tends to meet

new matter presented by the prosecution on rebuttal.” People v.

Terry, 720 P.2d 125, 129 (Colo. 1986).

3. Analysis

¶ 74 Bannan argues that in denying his request to call Dr. Lillehei

in surrebuttal, the trial court misapplied the law — and thus

abused its discretion — because the trial court misapprehended the

scope of its discretion. It did so, he argues, because the court

erroneously explained it could only allow surrebuttal if new matter

was introduced on rebuttal, but the law is that the court does have

discretion to allow surrebuttal even if new matter hadn’t been

presented on rebuttal. The People respond that the trial court

recognized it had discretion to allow surrebuttal even if rebuttal

37
didn’t introduce new matter and exercised that discretion to not

permit surrebuttal because there wasn’t a reason to do so based on

its assessment of the evidence.

¶ 75 To be clear, Bannan doesn’t contend on appeal that he sought

to call Dr. Lillehei in surrebuttal to respond to new information

presented by the People in their rebuttal case. Therefore, it was

within the trial court’s discretion to deny Bannan’s request for

Dr. Lillehei to testify in surrebuttal. People v. Martinez, 506 P.2d

744, 745 (Colo. 1973).

¶ 76 And we aren’t persuaded that the trial court improperly

exercised this broad discretion. To be sure, the trial court stated

that “it is appropriate to consider surrebuttal only in instances

where there is presentation in the rebuttal case of evidence that

then permits a surrebuttal case.” This, however, wasn’t a

misapplication of the law. The trial court didn’t say that it could

only permit surrebuttal if new matter had been presented on

rebuttal, as Bannan argues. Instead, the trial court explained when

it considered surrebuttal proper (i.e., “where there is presentation in

the rebuttal case of evidence that then permits a surrebuttal case”)

and then found that those circumstances weren’t present for

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Bannan’s case. This wasn’t an abuse of discretion by failure to

exercise discretion because the court, contrary to Bannan’s

argument on appeal, seemed to have exercised its discretion in

denying Bannan’s request. Put differently, the trial court didn’t

abuse its discretion by not allowing Bannan to call a surrebuttal

witness when the law didn’t require the trial court to allow him to

call such a witness and it explained that it didn’t believe the

proposed surrebuttal was proper for Bannan’s case, thereby

exercising its discretion.

¶ 77 Accordingly, we conclude that the trial court didn’t abuse its

discretion in denying Bannan’s request to call Dr. Lillehei in

surrebuttal.

G. Cumulative Error

¶ 78 Finally, Bannan contends that the cumulative effect of the

errors asserted on appeal requires reversal. “For reversal to occur

based on cumulative error, a reviewing court must identify multiple

errors that collectively prejudice the substantial rights of the

defendant, even if any single error does not. Stated simply,

cumulative error involves cumulative prejudice.” Howard-Walker v.

People, 2019 CO 69, ¶ 25.

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¶ 79 We have assumed that the trial court erred regarding

Bannan’s first issue on appeal. But we concluded that any error

was harmless and didn’t prejudice him. We reached this

conclusion because Bannan didn’t explain what his experts’

testimony would have been had the trial court allowed the experts

to testify to matters outside their reports. Without this offer of

proof, again, we’re unable to articulate how this missing testimony

prejudiced Bannan. Therefore, because there is no articulation of

prejudice to Bannan from the only error we assume on appeal, the

cumulative error doctrine doesn’t provide an independent basis for

reversal. See People v. Thames, 2019 COA 124, ¶ 69 (“[A] single

error is insufficient to reverse under the cumulative error

standard.”).

III. Disposition

¶ 80 The judgment is affirmed.

JUDGE GROVE and JUDGE JOHNSON concur.

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