"We are shocked and appalled to learn that Jesus Navarro Montes was recently released by a Mexican Judge," Chertoff said in a statement issued in Washington.
The Homeland Security secretary noted Navarro Montes is a suspect in the death of Border Patrol Agent Luis Aguilar, 32, who was killed in a "heinous act of violence" Jan. 19 near Yuma, Ariz., while trying to stop two vehicles that had illegally entered the United States and were heading back into Mexico.
"We are working with a determined Mexican government, and our Department of Justice, to seek swift justice for the Aguilar murder," Chertoff said. "We have also assured Agent Aguilar's family that every resource is being called upon in the relentless pursuit of justice."
The head of the union representing Border Patrol agents said a Mexican judge ordered Navarro Montes's release, WOLD-TV in Tucson, Ariz., reported.
Aguilar was run over at the Imperial Sand Dunes, Calif., about 20 miles west of Yuma, while putting down spike strips to stop Navarro's vehicle, the TV station said.