Friends and family said the last time they saw or heard from John Gamboa was Feb. 16, when he arrived in the capital.
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ABC Houston affiliate KTRK reporter Alex Bozarjian's numerous calls and conversations with the FBI on behalf of Gamboa's mother got the ball rolling on this.
Multiple sources confirm they're pursuing investigative leads both in the U.S. and in Mexico.
Fermina Gamboa, John Gamboa's mother, also said there was at least one withdrawal attempt from her son's account the day after he went missing.
"I am just saying that whoever holds my son, please let him go," Fermina Gamboa said.
It's been 12 grueling days for Fermina Gamboa, who spoke to KTRK last Thursday, pleading for her son's safe return from Mexico City.
ORIGINAL STORY: Family launches frantic search for Houston veteran who vanished during trip to Mexico City
Family is frantic after Houston man vanished during trip to Mexico
She told KTRK she was too distraught to speak on camera this week, but her message is still the same.
"Money can be replaced, but life cannot. We only have one life," she said.
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Multiple sources, including friends, now confirm a rough timeline of his movements before he went missing.
They said he arrived in Mexico City on the night of Feb. 16 and then took an Uber to his Airbnb. A friend provided KTRK with photos of his belongings left behind in the room.
At about 11:30 p.m., John Gamboa reportedly went to Montana's Disco and Bar alone. According to his friends, that's his last known location.
"I am not sure honestly if he's even alive," Fermina Gamboa said.
A missing person's flyer has since surfaced from La Fiscalia General de Justicia, Mexico's attorney general's office.
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Retired FBI agent Jim Conway said the feds can't conduct investigations in Mexico, but use liaisons to communicate with authorities.
"The national police, the attorney general's office, the intelligence office, whatever it may be, and the process of the investigation begins, as it does traditionally, of gathering evidence, looking at cell phone activity, talking to witnesses. That all takes place," said Conway, who's now president and managing director of Global Intel Strategies.
Sources confirmed to KTRK that multiple federal agencies are actively investigating.
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KTRK also made U.S. Rep. Lizzie Fletcher's office aware. They have since reached out to Fermina Gamboa.
Fletcher's office said in a statement:
"My heart goes out to John's mother, Fermina, and his loved ones during this difficult time. My team and I are monitoring the situation, and we are in contact with authorities about this ongoing situation. We will do everything we can to help bring John home."
Conway said the good news is that security services in Mexico City are relatively sophisticated, and they have historically had a good working relationship with the U.S.
"When I was there, we provided a lot of training, a lot of equipment under Plan Merida. We provided a lot of support to the Mexican security services, so hopefully that comes into play, and this will all have a happy ending," Conway said.
Fermina Gamboa said her son is a five-year Air Force veteran. She also said he gave her a double bone marrow transplant when she had cancer, which is a testament, she said, to what kind of man he is.
"He sacrificed himself just to extend my life," she said.