NEW YORK (CNNMoney) —It's every police chief's worst nightmare: An officer takes a gun off the street only for it to end up in the hands of another criminal.

Increasingly, departments are being encouraged -- and even required -- by state laws to sell the guns they confiscate instead of destroying them, sparking concerns that this scenario could be more likely.

The National Rifle Association, a vocal supporter of these laws, says the fear that a seized gun will get back into the hands of criminals is unwarranted since police departments take precautions to ensure that guns are sold to legal buyers.

But these safeguards aren't always foolproof. While a federal law makes it impossible to figure out how often these guns are ending up in the hands of criminals, CNNMoney identified four cases where this worst-case scenario happened.

http://www.kcci.com/project-economy/four-crimes-committed-with-guns-seized-and-sold-by-police/35958436