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.

In a letter, Senator Charles Grassley, R-Iowa, accuses the Justice Department - which oversees ATF - of trying to hide how long the suspects had been under watch.

The Justice Department responded by saying ATF "was not aware of" the suspect's purchase of the gun that killed Zapata when it happened. The agency says answering further questions would jeopardize the investigation.

Eight months after Jamie's death, the Zapatas haven't been given so much as an autopsy report.

"What are your thoughts on why you have so few answers?" Attkisson asked.

"I hope that it's not a cover up," Mary Zapata replied. "I pray that the weapon that killed my son didn't come from the United States and was allowed to travel to Mexico."

Desperate for answers, they've filed Freedom of Information requests with the very agencies whose leaders spoke at Jaime's funeral: ICE Director John Morton; Homeland Security Chief Janet Napolitano; and Attorney General Eric Holder.

"Agent Zapata's story is one that we must not forget, and it is one that we won't," Holder said at Zapata's funeral service. "He was a hero in every sense of the word."

When asked what her son might say now about his case, if he could talk, Mary Zapata replied, "A few days after he passed away, he came to me in a dream and he pointed to his lips. And he said, 'Mom, I cannot speak. You have to speak for me. Seek justice. Make sure another person does not have to go through what I went through.'"

ICE told Attkisson that the agency communicates regularly with the family and are doing all they can for them.

The three trafficking suspects recently agreed to plead guilty to weapons charges.

The Justice Department won't provide any information on arrests or identities of those suspected of actually shooting Zapata with the illegal weapon. An official also refused to comment on a report that Mexico may have just turned over the man believed to be responsible for the agent's death.