Whether investigation costs could be charged to Y. after a non-suit
No. In the absence of culpable conduct contrary to law, and without proof that Y. caused or hindered the proceedings, the costs could not be shifted to him.
Under Art. 158 CPP, costs after a liberating decision are admissible only if the accused caused the proceedings or impeded them through wrongful conduct causally linked to the costs. The file showed no such conduct; assigning costs would also contravene the presumption of innocence.