The official said the motive behind the killing remains unclear.

Officials with the US Embassy P90X in Mexico City declined to comment. At the US Justice Department in Washington, spokeswoman Tracy Schmaler law enforcement "continues to work closely with our Mexican counterparts to bring to justice individuals involved in these murders." US Embassy officials previously said that Enriquez was never in a position to provide visas and worked in a section that provides basic services to US citizens in Mexico. Mexican police provided no further details from Chavez's confession on how Enriquez might have helped provide visas to a drug gang. Enriquez was four months pregnant when she and her husband, Arthur H. Redelfs, were killed by gunmen who opened fire on their vehicle after the couple left a children's birthday party. Their 7-month-old daughter was found wailing in the back seat. Jorge Alberto Salcido, the husband of a Mexican employee of the consulate, also was killed by gunmen after leaving the same event in a separate vehicle.

Chavez told police that gunmen ray ban opened fire on Salcido because the two cars were the same color and the hit men did not know which one Enriquez was in, Pequeno said. Investigators also have looked at whether Redelfs may have been targeted because of his work at an El Paso County jail that holds several members of the Barrio Azteca, the gang believed to be responsible for the attacks. Pequeno said Chavez belongs to Barrio Azteca, which works for the Juarez cartel on both sides of the border. In March, US federal, state and local law enforcement officers swept through El Paso, picking up suspected members of the gang in an effort to find new leads in the killings. A suspect detained in Mexico shortly after the shooting confessed to acting as a lookout as the Azteca gang supposedly hunted down Redelfs, but he was never charged and was released without explanation. Officials also have speculated that both attacks could have been a case of mistaken identity.

More than 23,000 people have been blower killed in Mexico's drug-related violence since President Felipe Calderon launched an all-out offensive against drug gangs in 2006. Much of the violence stems from rival drug- and migrant-smuggling gangs vying for power, including a firefight Thursday that left 21 people dead and at least six others wounded about 12 miles (20 kilometers) from the Arizona border.