"From 2009-2011, the Phoenix Field Division of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), along with other partners, allowed illegal gun sales in order to track the sellers and purchasers, who were believed to be connected to Mexican drug cartels."
https://www.cnn.com/2013/08/27/world/americas/operation-fast-and-furious-fast-facts/index.html?no-st=9999999999
"Instead, it put into the hands of criminals south of the border some 2,000 weapons, which have been used to kill hundreds of Mexicans and at least one American, U.S. Border Patrol agent Brian Terry."
https://www.nationalreview.com/2016/01/fast-furious-obama-first-scandal/
"Terry’s death exposed Operation Fast and Furious, a Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) operation in which the federal government allowed criminals to buy guns in Phoenix-area shops with the intention of tracking them as they were transported into Mexico. But the agency lost track of more than 1,400 of the 2,000 guns they allowed smugglers to buy. Two of those guns were found at the scene of Terry's killing."
https://www.foxnews.com/politics/fast-and-furious-hearing-rips-holder-doj-for-deception-in-gun-running-scandal