Transcript for Boy shares what mother said when Mexican ambush began
And now, to the horrific and deadly ambush of Americans in Mexico, and tonight, just a short time ago, the FBI now confirming they will assist in the investigation. Mothers and children ambushed and killed. And for the first time right here tonight, we are hearing from that 13-year-old boy who walked 14 miles for help. What he says are the last words from his mother. ABC's Tom llamas again tonight. Reporter: Tonight, that 13-year-old boy credited with helping save his brothers and sisters, opening up about the deadly ambush in Mexico and what his mother said when the shooting started. To get down, right now. She was trying to pray to the lord and she was trying to start the car up to get out of there. Reporter: In an exclusive interview, Devin Langford and his father, David, telling us about the attack that took the lives of his mother and two little brothers. They just started the hitting car first, like with a bunch, a bunch of bullets. Reporter: The family believes the killers work for the drug cartels. Devin even remembering the weapons they had. Yeah, they were big guns and they were wearing masks. Afterwards, they got us out of the car and they just got us on the floor and then they drove Reporter: The children tried to flee, but as you see from this video, later, inside a hospital, most were too wounded. But the walk took several hours, so the kids sent out their 9-year-old sister, Mackenzie. I was kind of taking too long, because I was kind of hiding some of the time. Reporter: Devin eventually getting he up. My boy is a hero, simply because he gave his life for his brothers and sisters. Reporter: And like so many, he has the same question for the killers. Just why. Just why would you do that? Reporter: And tonight, a major development in the investigation. The Mexican government asking for the u.s.'s help, and now the FBI telling us they are getting involved and that they will, quote, help bring justice to the perpetrators of this heinous act of violence. David? Good to have you Bax from thank you, Tom.
This transcript has been automatically generated and may not be 100% accurate.