Instead of spent casing displaying a persons full name, show the gun's serial number. Police would be able to search a serial number and see information such as the category (rifle, handgun, shotgun), the exact model, the legal purchaser, and the store it was bought from. This would make it so police/detectives have to investigate further than just issuing a warrant to someone's full name on a spent casing. There could also be a npc/tool that scrapes off serial numbers or have them scraped by default if bought from the illegal arms dealer.