Leads in a federal multi-state search for firearm parts stolen from a Bureau of Alcohol, Tobacco, Firearms and Explosives facility have led agents to a gun dealer in Virginia who was sold some of the stolen firearm parts, according to federal law enforcement sources.

The search for thousands of stolen gun parts and an unknown number of guns is intensifying. ATF officials say they are moving quickly to track down the stolen property and they have stepped up security at the ATF facility in Martinsburg, West Virginia where the theft occurred.

ATF officials say they have now recovered a significant number of the stolen parts and guns, but law enforcement sources say there are still many out on the streets that pose a "risk to public safety."

Get Breaking News Delivered to Your Inbox

The search has stretched nationwide and now the U.S. Senate is demanding answers.

In a letter to the ATF deputy director, senators on the Senate Homeland Security and Governmental Affairs Committee have asked for an accounting of what was taken out of the ATF facility. The letter, which was signed by Chairman Ron Johnson, R-Wisconsin, and Ranking Member Gary Peters, D-Michigan, seeks to determine when the ATF found out about the security breach and whether any of the stolen property has been used in crimes.

"The ATF is tasked with ensuring public safety, and this episode raises significant concerns. We need a full accounting of the situation and I hope the ATF responds quickly to my letter," Johnson said in a statement.