A West Virginia man pleaded guilty to stealing thousands of guns and firearms parts right under the nose of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

In a little-noticed plea agreement submitted April 24, Christopher Lee Yates, 52, admitted to taking weapons and parts from the ATF’s National Firearms and Ammunition Destruction Branch in Martinsburg, where he had worked as a contracted security guard since at least 2013. Yates’s haul included handguns, semiautomatic rifles, unregistered machine guns, ammunition magazines, bullets, and scopes. He also stole at least 3,000 pistol slides from former ATF service weapons that were slated for destruction.

The long-running theft represents the most significant failure by the ATF to secure weapons under its control since the Fast and Furious scandal in 2011. The agency has recovered at least 4,000 stolen parts and guns so far.

In March, Senators Ron Johnson of Wisconsin and Gary Peters of Michigan sent a letter to the ATF to demand a full accounting of the theft. Though the ATF says it has sent a response to the senators, the agency claims it is bound from releasing it. Aides to the senators have not responded to repeated requests for the letter or comment on its content.

Yates was arrested in February after ATF agents discovered that a pistol slide recovered by the police in Philadelphia was from a decommissioned service weapon that should have been destroyed at the Martinsburg facility. At least 31 of the weapons stolen by Yates had been sent to Martinsburg for destruction after they were recovered during criminal investigations. Nine of the guns should have been registered under the National Firearms Act, which regulates possession and sale of certain weapons like machine guns and short-barreled rifles. Law enforcement officials also found nearly $40,000 cash during a search of Yates’s home.

Yates’s attorney, Kevin Mills, declined to comment.

The plea agreement says Yates stole the weapons and parts from the Martinsburg facility before his coworkers arrived for work. It does not explain why the items in question were vulnerable to theft in the first place. ATF policy dictates that weapons slated for destruction are to be stored in a locked vault with limited staff access. Two staffers are also supposed to witness a gun’s disposal and sign a document certifying their presence. The ATF has declined to comment on whether any other employees of the Martinsburg facility were fired or have resigned as a result of the theft.

Two men told authorities they bought weapons from Yates. Adam Schreiber of Bedford, Pennsylvania, told ATF agents he bought 15 rifles, at least 80 handguns, and 10 to 15 lower receivers for AR-style rifles, which can be turned into completed firearms with unserialized parts not subject to background check requirements. Schreiber hung up when reached by phone. Anthony Miller, who worked alongside Yates at the ATF facility, bought two stolen pistols from the guard, according to the agreement. Attempts to reach Miller by phone were unsuccessful.

Neither man has been charged with a crime. The U.S. Attorney’s Office for the Northwest District of West Virginia declined to comment on whether anyone else was subject to ongoing investigations stemming from the theft.

Following his guilty plea, Yates was released to house arrest. He will be sentenced in late August, and faces up to 10 years in prison for each of the two guilty pleas.