From The Truth About Guns:

The report is a synopsis of a larger, previously posted report called, “Police departments sell their used guns. Thousands end up at crime scenes.” In that report, the author nearly got to the truth about how the guns wind up in criminals’ hands, but also left out the most important part.

“Once sold by a department, weapons enter a secondary market where they can be resold to members of the public or other dealers,” the report stated. “By the time they turn up at crime scenes, the guns may have been stolen, traded or resold multiple times with little documentation. They sometimes still have the departments’ name stamped on the side.”