WASHINGTON — Ten members and associates of a Southwest border gang have been charged in the United States in the murders a year ago of a U.S. consulate employee, her husband and another man in Juarez, Mexico.

A grand jury indictment unsealed Wednesday in El Paso, Texas, revealed federal charges against 35 people in all, allegedly linked to the Barrio Azteca gang, including the 10 charged in the murders.

The indictment details a criminal enterprise that began in the late 1980s as a violent prison gang, which then expanded into a group of murderers and drug traffickers who operate on both sides of U.S.-Mexico border.

Twenty-three of the alleged gang members were based in the United States; 12 in Mexico. Twenty-eight are in custody. Seven are fugitives.

The charges represent "our continued action to ensure safety along our Southwest border," Attorney General Eric Holder told a news conference.

The case is an important step in dismantling "one of the most violent gangs" along the Southwest border, said FBI Executive Assistant Director Shawn Henry.

The unsealed indictment did not supply a motive for the killings of the consulate employee, her husband and the other man, but it could have been as simple as a case of mistaken identity, said Assistant Attorney General Lanny Breuer, who heads the Justice Department's criminal division.

The slayings were so brutal, the motive is almost irrelevant, said Holder.

Consulate employee Leslie Ann Enriquez Catton and her husband, Arthur H. Redelfs, were killed on March 13 of last year when gunmen opened fire on their sport utility vehicle after they left a birthday party.

Jorge Alberto Salcido Ceniceros, the husband of a Mexican employee of the consulate, also was killed by gunmen after leaving the same event in a separate vehicle.

Seven of the 10 defendants charged in the murders are in custody in Mexico. The other three are fugitives.

To increase its power, Barrio Azteca formed an alliance with the Vicente Carrillo Fuentes drug trafficking organization in Mexico and conducted enforcement operations against VCF rivals.

Since Jan. 1, 2003, the indictment alleged, the defendants engaged in extortion, money laundering, kidnapping and the murder of five other people in addition to the murders of the U.S. consulate employee, her husband and Ceniceros.