LOS ANGELES–Eric Harden, the head of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives Los Angeles Field Division (ATF) sent out a memo on March 31 to Southern California police departments, stating that the agency found that law enforcement officers have been illegally buying and reselling guns. These actions could be a direct violation of federal firearm laws.

According to the Los Angeles Times, Harden showed concern about “the growing trend of law enforcement officials engaging in the business of unlicensed firearms dealing,” and described it as an “emerging problem.”

The memo focuses on the resale of “off-roster” firearms, which are unapproved to be sold to, or bought by the general public.

“It is our goal to educate, not investigate, to ensure law enforcement officials comply with federal law in order to avoid unnecessary public embarrassment to themselves and your Department/Agency,” Harden wrote in the memo.

According to the Los Angeles Times, the memo does not say how many officers have been affiliated with the violation, but that over 100 firearms have been bought by officers and some of those firearms have been involved in crimes.

California law has an exemption noting that sworn peace officers are allowed to purchase these firearms that the general public cannot. Another exemption states that under certain circumstances, officers can resell the guns, but they can never be bought or sold for profit as a business unless they hold a federal firearms license (FFL). The memo targets the officers who do not hold this license.

If caught selling firearms without a license, the offense carries a 5-year maximum sentence in prison. In addition, lying on a federal form is an offense that carries a maximum 10-year penalty. It is unclear when the ATF found the problems, or what prompted the memo.

The federal prosecution of the sale of “off-roster” firearms by state law enforcement officers is rare. The most recent offense happened in June 2015 in the county of Sacramento, when former Sheriff’s Deputy Ryan McGowan was found guilty of selling firearms illegally and falsifying records.

The Los Angeles Times reported that Ginger Colbrun, the spokeswoman for the ATF Los Angeles Office indicated that the offenses were first noticed when some of the firearms found at crime scenes were traced and found to be bought within the last 3 years.

The national average of the time frame from when a gun is bought from a licensed dealer to when it is found in a crime scene is 10 years. Some of the weapons were bought within the last 3 years, which indicates that they were “straw purchases,” which is when an item is bought in order to be sold quickly. According to reports, this trend prompted the ATF to take a closer look.

“After further investigation, ATF noticed some law enforcement officers had been making significant purchases of firearms,” Colbrun said.

The ATF has not confirmed the agencies of the officers being investigated. The investigations are ongoing.