The families of two U.S. immigration agents shot more than a year ago on a Mexican highway renewed their demand Friday that the U.S. government explain the decisions that put them there and answer questions about how guns purchased in the U.S. fell into the hands of their attackers.

The parents of slain Immigration and Customs Enforcement agent Jaime Zapata joined with the sister of agent Victor Avila to press the government on whether an operation similar to one in Arizona that allowed illegally purchased guns to be smuggled into Mexico in hopes to tracking them to higher-ranking criminal figures was responsible for the guns used in the attack. Two of the weapons have been traced to illegal purchases in Texas.

The families spoke in Zapata's hometown of Brownsville, one day after the U.S. House voted to hold Attorney General Eric Holder in contempt for not providing documents relevant to an investigation of so-called Operation Fast and Furious in Arizona. In that case, agents with the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives lost track of hundreds of weapons they had hoped to trace higher in criminal organizations. Justice Department policy had long forbid such "gun walking" and two guns from that operation were found at the scene of the slaying of U.S. border agent Brian Terry.

"I feel that I owe my son justice and I still haven't gotten it," said Mary Zapata, the slain agent's mother, wearing a lapel pin with her son's picture.

Earlier this month, Zapata's family filed a $25 million wrongful death claim against the U.S. government. Avila is seeking $12.5 million claiming negligence and intentional infliction of emotional distress. The claims are an initial step toward lawsuits. They note that at least two weapons used in the attacks originated in Texas and were passed to cartel gunmen in Mexico by known gun runners in the U.S.

"I do believe that guns that were walked through the Dallas area especially were responsible," said Mary Zapata.

Tom Crowley, a spokesman for the Dallas field division of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, said the agency "has always said that this investigation has no connection whatsoever to Fast and Furious."

Crowley denied the agency knew about the Dallas-area gun purchase beforehand.

"We had no knowledge of the Oct. 10, 2010, purchase of that weapon prior to the transaction; we had no idea the transaction was going down," said Crowley.

Zapata and Avila were on their way back to Mexico City on Feb. 15, 2011, after meeting a colleague in San Luis Potosi to pick up equipment. They were driving an armored black Chevrolet Suburban when two SUVs carrying gunmen ran them off the road. Once they placed the Suburban in park, the door locks automatically opened. In the struggle to close the door, a window was opened and shots were fired into the vehicle, killing Zapata and wounding Avila.

People involved in the illegal purchase of the guns used in the attack have been convicted in U.S. courts. One person allegedly involved in the attack, Julian Zapata Espinoza, has been extradited to the U.S. and awaits trial in Washington, D.C., on murder charges.

Attorneys for both families say the U.S. government has told them little since the days immediately following the attack. Trey Martinez, one of the lawyers, said some of the outstanding questions include why the agents were on the road after sharing their safety concerns with superiors; whether superiors were aware of a flaw in the armored vehicle that automatically unlocked the doors; and why an alternative diplomatic service wasn't used to transfer the equipment.

Magdalena Villalobos said her brother's physical wounds have healed, but he is still recovering emotionally from the attack during which 90 shots were fired into the vehicle. She said her brother is receiving treatment to move past it.

"Being there when Jaime expired has been an incredibly difficult thing for him to try to wrap his mind around," she said.


Associated Press writer Pete Yost in Washington, D.C. contributed to this report.