Murdered U.S. agent's family wants answers

The murder of U.S. Special Agent Jaime Zapata on assignment in Mexico happened more than eight months ago, but has been shrouded in mystery.

Not a day goes by that Amador and Mary Zapata don't think about their son Jaime, a Special Agent with Immigration and Customs (ICE).

"I think about a young man with a loving heart who loved fishing, who loved family and friends," said his mother Mary.

Jaime was one of five brothers, all in the field of criminal justice. Earlier this year, he was sent to Mexico City on what he said would be a "safe" assignment.

"He had told us that he was going to be detailed to Mexico, that he was going to be working out of the embassy, that he was going to be in an armored vehicle," said his father Amador.

But on Feb. 15, Zapata and his partner Victor Avila were attacked in their government SUV by suspected Mexican cartel members.

Nobody knows exact details, but the ICE agents were traveling hundreds of miles from their Embassy assignment on a notorious stretch of highway, believed unarmed with no escort. Their vehicle was cut off and bandits attacked. Both agents were critically injured by gunfire.

Fellow agents told the Zapatas Jaime had been hurt. Mary phoned relatives to ask for prayers.

"When I got off the phone, my son says, 'Mom, Jaime is dead,'" she recalled.

"It was horrible," said Amador. "And to this day, I still think of it and it devastates me."

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What upsets the couple most is their belief that U.S. law enforcement could have stopped the sale of a gun used to kill their son.

CBS News investigative correspondent Sharyl Attkisson has obtained law enforcement records that show the gun that killed him came from the U.S., and the suspects who allegedly trafficked the firearm had been under law enforcement's watch for months in Dallas - even videotaped taking part in trafficking crimes.

Three traffickers who provided that weapon had been on law enforcement's radar screen five months BEFORE Jaime was shot. ATF had traced them to a cache of illegal firearms being smuggled to Mexico, yet apparently made no move to question or charge them.

Trace reports show the suspects then trafficked dozens more weapons, including the gun used against Zapata, and they even transferred 40 illegal firearms to a DEA and ATF informant.

But they were only arrested months later, after Zapata was killed.

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    Sharyl Attkisson is a CBS News investigative correspondent based in Washington.