PHOENIX (AP) — A Mexican man accused in the killing of a U.S. Border Patrol agent has admitted he was part of a crew that sneaked into the United States to find marijuana smugglers to rob at the time of the fatal shooting.

Manuel Osorio-Arellanes pleaded guilty Tuesday in the death of Agent Brian Terry. He said the group got into the country a week before the shootout that killed Terry, and stashed guns and food supplies on the U.S. side of the border.

Authorities haven't said which member of the rip-off crew was believed to have fired the fatal shot at Terry on Dec. 14, 2010. Of the five men charged in Terry's murder, two are in custody, and three others remain fugitives.

Prosecutors agreed not to seek the death penalty against Osorio-Arellanes, who could face life in prison for the first-degree murder conviction.

Terry's death revealed the botched "Fast and Furious" gun-smuggling operation, marking the biggest conviction to date in a case that embarrassed the federal government and prompted a series of congressional investigations.

"Operation Fast and Furious" was launched in 2009 to catch trafficking kingpins, but federal agents lost track of about 1,400 of the more than 2,000 weapons — including AK-47s and other high-powered assault rifles.

Federal authorities faced criticism for allowing suspected straw gun buyers to walk away from shops with weapons, rather than arrest the suspects and seize the guns there.

Two rifles bought by a gun-smuggling ring that was being monitored through "Fast and Furious" were found at the scene. But authorities have declined to say whether the murder weapon in Terry's death was linked to a purchase from the operation.

Terry and three other agents came under attack in a canyon north of the Arizona border city of Nogales by Osorio-Arellanes and four other men, investigators have said.

Osorio-Arellanes, of El Fuerte in the Mexican state of Sinaloa, was shot during the gunfight and has been in custody since the shooting. He told investigators he raised his weapon toward the agents during the shootout but didn't open fire, the FBI said.

Sentencing has been set for Jan. 11 before U.S. District Judge David Bury. Osorio-Arellanes' attorney, Clay Hernandez, declined through an assistant to comment on Tuesday on the plea.

"Today's plea is an important step in seeking justice on behalf of Agent Terry," Laura Duffy, the top federal prosecutor in San Diego whose office is prosecuting the case, said in a statement.

Some of the guns purchased illegally through "Operation Fast and Furious" were later found at crime scenes in Mexico and the U.S. Critics have hammered federal authorities for allowing informants to walk away from Phoenix-area gun shops with weapons.

The two guns found at the scene of the Terry shooting were bought by a straw buyer for a smuggling ring suspected of purchasing guns for the brutal Sinaloa cartel, according to investigators.

Jaime Avila, 25, has admitted in court to buying the two guns and has pleaded guilty to gun charges in a smuggling case separate from the prosecution into Terry's death. Avila, who isn't charged in Terry's death, faces up to 10 years in prison when he's sentenced on Dec. 12.