ST. LOUIS–In 2022, St. Louis police reported seizing 27 devices, which when installed on a pistol or a rifle, can turn them into illegal fully-automatic machine guns. Just five days into the new year, the department says it has seized three already, on pace for 150 in a full calendar year. Four were found in 2021.

Interim Police Chief Michael Sack joined federal counterparts Thursday in warning the public about the modifications, which the U.S. Attorney’s office has now linked to the death of a 16-year-old at a St. Louis loft apartment in March.

The so-called “after-market” devices aren’t made by firearms manufacturers and according to law enforcement authorities, are only going to be recognized by a trained eye.

Brent Beavers, Assistant Special Agent in Charge with the St. Louis office of the Bureau of Alcohol, Tobacco and Firearms, told reporters Thursday that after training sessions with St. Louis area law enforcement agencies, those departments went back into their evidence rooms and found the devices on seized weapons.

“That just makes our jobs more dangerous, more difficult and it is a significant challenge not only to our agency but any other agency as well. Certainly people are allowed to own, carry and possess firearms but not modified or having any of these devices placed inside them,” Sack said. 

“I don't know any reason why somebody would carry a weapon with such a device on the street,” he added before authorities demonstrated how the recoil from firing shots affects accuracy. Any shooting, he said, can turn into a homicide with devices that authorities say can fire off 20 shots in under five seconds. 

U.S. Attorney Salyer Fleming noted an increase in prosecuting cases involving the devices and said Thursday's news conference was meant to put those who use them "on notice". A conviction for using them carries a minimum 30 year sentence. 

Eight people were arrested in the Cape Girardeau area last fall as part of an ATF probe into the sale of the devices.

On Wednesday, U.S. Attorneys in Texas charged a man there accused of selling them on Instagram.