Legal Implications of a fish

Hello all, recently I got a work promotion that I was competing for with a fellow coworker.

Last week they did a no call no show to work leaving the whole team baffled. This week I noticed a nasty smell in my office and cleaned the whole place out. I checked the ceiling tiles and found a bag with dead fish in it. Whole place smells nasty now.

I have no proof it’s him, but want to know the legal implications if I can get HR/Police to contact him and he admits it.

Does anyone know the best strategy here? I know it’s just a prank, but I want to make sure he doesn’t get away with the damage he’s done.

Location: Colorado, US