SAN DIEGO -- A 17-year-old Mexican national pleaded guilty Friday to a murder charge for the shooting death last summer of a U.S. Border Patrol agent near Campo.

Christian Daniel Castro-Alvarez appeared before a federal judge in San Diego and admitted that on the evening of July 23, he illegally entered the United States to rob a Border Patrol agent of government property.

U.S. Border Patrol Agent Robert W. Rosas Jr. was lured out of his vehicle by Castro-Alvarez and unidentified co-conspirators, and during the struggle that ensued, the 30-year-old victim was shot multiple times, according to prosecutors.

Castro Alvarez was 16 years old at the time of the shooting, 10News' Itica Milanes reported.

Authorities have not said whether they have made any other arrests or know the identities of Castro-Alvarez's accomplices.

FBI Special Agent in Charge Keith Slotter said the investigation into Rosas' killing is ongoing.

The guilty plea from Castro-Alvarez marks a significant day in the case, he said.

"The night Agent Rosas was killed, we all lost a brave officer whose mission was to defend our country from threats, both domestic and abroad," Slotter said. "We recognize the ultimate sacrifice Agent Rosas paid protecting this country."

Department of Homeland Security Secretary Janet Napolitano said the plea by Castro-Alvarez makes it clear that those who harm law enforcement personnel will be swiftly brought to justice and punished.

"I am confident that others involved in Agent Rosas' tragic death will also be held responsible, and I applaud the U.S. Attorney's Office and the FBI, as well as the government of Mexico for their cooperation in the case," she said.

"The devoted men and women of Southern California's law enforcement and first-responder community deserve our deepest appreciation for their support of Agent Rosas' family and his Border Patrol colleagues over the past four months."

Castro-Alvarez faces up to life in prison when he is sentenced Feb. 19 by U.S. District Judge M. James Lorenz.