Four takeaways from our investigation into police agencies selling their guns

About nine times a day over two decades, a gun used in a crime has been traced back to its original owner: a law enforcement agency. 

A joint investigation by CBS News, The Trace, and Reveal from the Center for Investigative Reporting has found at least 52,000 such incidents and identified more than 140 police agencies that sell or trade in their guns, allowing dealers to then resell them. 

Here's a look at the key findings of the investigation. You can read and watch the complete investigation here.