You know the funny thing about these “ghost guns” is they are untraceable so you don’t know where they came from. The best way to pin them to someone is to “pin” them to that person. This can be through forensics or proximity. In this case the suspect just happens to have a gun whose origins are unknown. Very convenient.
You’re questioning how innocent people being imprisoned or executed is related to false evidence? OK, here one that’s specific to planting evidence.