Homeland Security Secretary Janet Napolitano on Monday said an indictment against three illegal immigrants accused of killing a border patrol agent sends a "clear message" to drug cartels and border smugglers.

A federal judge unsealed a 14-count indictment against Manuel Osorio-Arrelanes and two other Mexican natives last Friday, accusing them of participating in the shooting that killed 40-year old Border Patrol agent Brian Terry in December.

"This indictment also sends a clear message to those who would consider committing violence against the Border Patrol: we will not stand for aggression against our men and women in uniform, and we will bring the full resources of the federal government to bear in protecting them from harm and holding accountable those who would threaten their lives or their safety," said Napolitano in a statement.

The indictment alleges that the group of men had been robbing illegal immigrants on the U.S. side of Arizona’s southwest border, and when several border patrol agents tried to detain the men, they opened fire, shooting and killing Terry with an AK-47.