For Amador Zapata, the father of slain ICE Special Agent Jaime Zapata, it's the phone calls he misses most.

Jaime, 32, would call him up almost every day and joke around. "Are you behaving, Dad?"

Jaime's mother, Mary Zapata-Muñoz, misses the impromptu barbecues, the days Jaime would come over to their home in Brownsville and light up the grill in the backyard and invite his brothers and a bunch of friends over.

In the eight months since Jaime Zapata was killed in an ambush in Mexico that also wounded another ICE agent, his parents say they have been proud to see his life eulogized by top U.S. government officials and to see a highway, a road and even a boat ramp named after their son.

But they also have grown increasingly frustrated in their quest to get answers about his death. They want to know why he was in northern Mexico when he initially was told that his assignment was intelligence gathering in the U.S. Embassy in Mexico City.

They want to know more about the guns used in the attack, and whether any of them were tied to the U.S. government's Operation Fast and Furious, which failed to track weapons that ended up in the hands of Mexican cartel members.

"I feel like I'm not getting the truth," his mother said Friday in an interview with the Houston Chronicle. "I know nothing will bring my son back. No truth. No nothing. But I want to make sure that no other person has to go through what we went through, what Jaime went through. Can you imagine those last moments, trying to save your life and your buddy's life? What it must have been like?"