The hero teenage boy who walked 13 miles in the desert to get help for his bleeding siblings after Mexican cartel gunmen opened fire on them last week has told how they spared his life by telling him to lie on the ground before driving away after slaughtering his mom and two brothers.

Devin Langford, 13, was in a car with his mother and siblings when the gunmen sprayed bullets on his family in the Mexican state of Sonora last week. Nine people died in the massacre, which FBI sources say was a 'targeted assassination' but for which no motive has yet been given.

Police continue to investigate why the family, which had been living in a self-contained religious community for years, became the drug gang's victims.

Among those killed was his mother, Dawna, and two of his siblings. The others - including his baby brother - were injured.

On Monday, Devin cried during an interview with Good Morning America as he recalled how the gunmen rained a hail of bullets on the family.

'Afterwards they got us out of the car and got us on the floor and drove off,' he said.

The gunmen then drove away, leaving him and the other surviving children helpless. He walked 13 miles to find help after hiding his younger, wounded siblings in bushes.

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Devin Langford, 13, walked 13 miles to find help for his injured siblings after Mexican cartel gunmen opened fire on his family in Sonora last week, killing his mother and two of his brothers along with six other people from their Mormon community

Devin wept as he described fearing that he was being followed during his walk to find help. He was joined for the interview by his father David, who was not in the car. He has moved the rest of his family to America

.@ABC NEWS EXCLUSIVE: Hero teen in deadly Mexico massacre speaks out. “It felt like a lot of bullets.” @TomLlamasABC has the story. https://t.co/6q46Ko84We pic.twitter.com/wRzAiEsKne — Good Morning America (@GMA) November 11, 2019

Devin said he feared he was being followed and that someone else would shoot him as he walked.

He detailed the horrific shooting, starting with the 'bunch of bullets' which descended on his family's car.

'They just started hitting the car first, bunch of bullets just started shooting rapidly at us,' he said.

He said he believes the cartel members deliberately shot out the car's engine to stop them from being able to escape. His mother, he said, frantically tried to restart the vehicle.

'The car didn't work so, she was trying to start to car but I'm pretty sure they shot something so the car wouldn't even start to get down right now, she was trying to pray to the Lord and start the car up to get out of there,' he said.

Once the men had gone, he walked 'a little while' carrying his youngest brother, nine-month-old baby Brixton, but had to put him down.

'I walked a little while until I couldn't carry him no more so we put him in a bush.

'Every one of them were bleeding really bad. I was trying in a rush to get there,' he said.

During his walk to find help, he said he battled the fear of being followed with the shock and trauma of having just seen half his family being slaughtered.

'That there wasn't anybody else out there trying to shoot me or follow me or about my mom or my two brothers that died,' he answered, when asked what he was thinking before finding help.

Dawna Langford and one of her sons, Trevor, who died (left). Two-year-old Rogan (right) was also killed

This was what remained of one of the vehicles. The cars went up in flames after being pounded by bullets

Nine-month-old baby Brixton Langford was left with an open flesh wound when he was shot in the chest

Kylie, 14, was shot in the foot (left) and eight-year-old Cody was shot in the back

Four-year-old Xander was also shot in the back but miraculously survived the massacre

His grieving father, David, said his son was a hero.

'He's really a hero, he definitely saved his little brothers and sisters. I think he did it because of his love for them. My boy's a hero simply because he gave his life for his brothers and sisters.

'Every one of my children that survived that are living miracles.

'How many bullet holes were fired into that vehicle… at that horrific scene and how many children were involved. It's amazing. It's amazing. It's beyond amazing that they survived,' he said.

He lamented having to move and said the family now has nowhere to go.

'Not only have I lost a wife and two children but having to move the rest of my family with really no place to go...

'My message is to hold on to your family. There's nothing like family,' he said.

The family buried Dawna and her two sons in La Mora on Thursday.

'The toughest part for me was saying goodbye… saying goodbye to two innocent lives that were cut short and a vibrant wife that lived a life to its fullest that had many friends and and was loved by all by everybody,' David said.

Devin (center in red shirt) helped carry a coffin during the funeral service last Thursday for his mother and two brothers

The family buried Dawna and her two sons in La Mora on Thursday. David is pictured above being comforted by relatives during the funeral service

A mourner holds a remembrance card at the funeral ceremony for Dawna Ray Langford, 43, and her sons Trevor and Rogan, who were among nine victims killed

'I believe in forgiveness, but I also believe in justice and forgiveness doesn't rob justice.

'You don't get justice too much in Mexico.'

Five of Dawna's children were injured in the attack and were airlifted to an Arizona hospital for treatment.

Nine-month-old baby Brixton Langford was left with an open flesh wound when he was shot in the chest.

David said if the bullet had struck the baby just a quarter of an inch lower it would have struck his lung.

Kylie Langford, 14, was shot in the foot and nine-year-old Mckenzie Rayne Langford was shot in the arm.

Eight-year-old Cody Greyson Langford was shot in the jaw and four-year-old Xander was shot in the back.

Also killed in the attack was Christina Marie Langford Johnson and Rhonita Miller and her four children - six-month-old twins, Titus and Tiana, her 10-year-old daughter Krystal and 12-year-old son Howard.

Men were spotted digging a mass grave on Thursday in La Mora ahead of the funeral for Dawna and her sons

Soldiers assigned to Mexico's National Guard stand by a bullet-riddled vehicle belonging to one of the mothers gunned down in the cartel ambush that killed nine

Mexico on Sunday invited the FBI to participate in the investigation of the attack.

The Foreign Ministry said it made the invitation through a diplomatic note to the U.S. embassy in Mexico.

'The Mexican government reiterates its commitment to investigate the facts, in order to... offer justice to the affected families,' it said in a statement.

The U.S. agents must work in coordination with their Mexican counterparts and will not be armed, it added.

In a statement, the FBI said it would assist in the investigation, adding, 'The FBI remains committed to working alongside our international partners to help bring justice to the perpetrators of this heinous act of violence.'

An FBI source told The New York Post last week that the victims were 'taken out of their cars and shot in a targeted assassination.'