Mexico City ? A drug-cartel enforcer told Mexican police that a rival gang infiltrated the biggest U.S. consulate along the border through a worker who helped get them U.S. visas, and that he ordered her killed for it. An American official rejected the claim Friday and said the motive for the slaying remains unknown.

Jesus Ernesto Chavez, known as “El Camello”, second from left, stands as he is guarded by a federal police officer during a presentation to the press Friday in Mexico City.

The employee, Lesley Enriquez, was among three people connected to the U.S. consulate in Ciudad Juarez who were killed March 13 in attacks that raised concerns that Americans were being caught up in the drug-related violence raging in that border city and across Mexico.

Jesus Ernesto Chavez, whose arrest was announced Friday, confessed to ordering the killings, said Ramon Pequeno, the head of anti-narcotics for the Federal Police. Pequeno said Chavez leads a band of hit men for a street gang tied to the Juarez cartel.

Enriquez and her husband were killed in Ciudad Juarez, across the border from El Paso, Texas, as they drove toward a border crossing. Chavez also is accused in a nearly simultaneous attack that killed the husband of a Mexican employee of the consulate.

Pequeno said Chavez told police that Enriquez was targeted because she helped provide visas to a rival gang.

A U.S. federal official familiar with the investigation said Friday that after the killings, U.S. officials investigated possible corruption involving Enriquez and found none. The official was not authorized to speak about the case and spoke on condition of anonymity.

The official said the motive behind the killing remains unclear.

Officials with the U.S. Embassy in Mexico City declined to comment. At the U.S. Justice Department in Washington, spokeswoman Tracy Schmaler said law enforcement “continues to work closely with our Mexican counterparts to bring to justice individuals involved in these murders.”

U.S. Embassy officials previously said that Enriquez was never in a position to provide visas and worked in a section that provides basic services to U.S. 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 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, U.S. 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 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 from the Arizona border.