More than 68,000 illegally trafficked firearms in the U.S. came through unlicensed dealers who aren’t required to perform background checks over a five-year period, according to new data released Thursday by the Bureau of Alcohol, Tobacco Firearms and Explosives, Ednews reports via AP.

That represents 54% of the illegally trafficked firearms in the U.S. between 2017 and 2021, Justice Department officials said. The guns were used in 368 shooting cases, which are harder to investigate because unlicensed dealers aren’t required to keep records of their sales that could allow federal agents to trace the weapon back to the original buyer, said ATF Director Steve Dettelbach.

The report ordered by Attorney General Merrick Garland is the first in-depth analysis of firearm trafficking investigations in more than 20 years. It examined more than 9,700 closed ATF firearm trafficking investigations that began between 2017 and 2021. Firearms trafficking is when guns are purposely moved into the illegal market for a criminal purpose or possession.

The second-highest share of firearm-trafficking cases investigated by ATF was straw purchases, when someone buys a gun for a person who can’t get it legally themselves.