U.S. Border Patrol Agent Brian Terry was killed in 2010 during a firefight with an alleged rip-off crew near Nogales. Two rifles being monitored by the government as part of its "Fast and Furious" operation were found at the crime scene.
Manuel Osorio-Arellanes and four other Mexican nationals have been charged in Agent Terry's killing. However, three of the four are still fugitives.
On Tuesday, Osoroio-Arellanes entered into a plea agreement with prosecutors, pleading guilty to first-degree murder, The Associated Press reports.