(CNN) -- A Mexican man pleaded guilty on Tuesday to first degree murder in the death of Border Patrol Agent Brian Terry, the first conviction in a case with an indirect link to the politically charged "Fast and Furious" gun-running operation.
Manuel Osorio-Arellanes, 36, admitted that on the night of December 14, 2010, he and four others were looking for drug traffickers to rob them of marijuana.
The group encountered Terry and other Border Patrol agents along Arizona's border with Mexico and a gun battle broke out.
In his plea agreement, Osorio-Arellanes agreed the shot that killed Terry was fired by a member of his group although he did not claim to have personally fired the shot or blame someone else specifically for the crime.
The Terry case has been controversial because two rifles from the "Fast and Furious" operation were found at the scene of his killing. But U.S. officials have not produced evidence proving that Terry was killed with either of those guns.
Osorio-Arellanes was wounded and arrested at the scene. He appeared in court in Tucson on Tuesday to plead guilty to one count of first degree murder. As part of the deal prosecutors agreed not to seek the death penalty and dropped other charges against him.
He faces up to life in prison when sentenced in January.
Four others were charged with roles in the gun battle and Terry's death, including one who was captured in Mexico in September and is awaiting extradition. The other three remain at large.
"Agent Terry was killed in the line of duty courageously safeguarding our border," said Laura Duffy, U.S. Attorney for the Southern District of California. "Our country owes him and his family a great debt of gratitude for his ultimate sacrifice in service to our country. Tuesday's plea is an important step in seeking justice on behalf of agent Terry."
The Bureau of Alcohol Tobacco Firearms and Explosives began "Fast and Furious" in 2009 with the purpose of tracking around 2,000 weapons intended for drug cartels. But things went awry when agents lost track of more than half of those weapons.
A September report by the Justice Department's inspector general said the anti-gun trafficking operation was marked by "a series of misguided strategies, tactics, errors in judgment and management failures" that allowed hundreds of weapons to reach Mexican drug cartels.