I ran a gun store for several years. Finally, we were robbed, when they ran the serial numbers I had 2 that had been reported stolen.
I was surprised to find out that it was a pair of handguns that one of my buddies traded in. Since we had to trace them back, I asked where he got them, he bought them both from a Missouri city cop. You can pretty much guess where he came up with two handguns previously reported stolen.
Like cocaine disappearing from the evidence room. Poof!