Transcript for Arrest made after deadly ambush that killed US family in Mexico
The brutal attack leaving six children and three mothers dead but miraculously some of the kids were able to escape and Tom llamas from Mexico has more. Reporter: Police making that arrest here in sonora where this happened and they made the arrest up near the border and one of the reasons why they're looking at the suspect is because he had two hostages. He also had an arsenal of weapons, several high caliber rifles were in his truck. Now, we do want to caution this is very preliminary in the investigation and the bloodthirsty thugs who did this had several hours to get away after they committed that massacre. This morning, ABC news learning new details about that ambush attack on an American family in Mexico. Overnight relatives visiting the horrific crime scene that looks like something out of a war. This all that remains of one of their SUVs. Mexican officials believe drug traffickers attacked the family possibly confusing them as a rival gang. I believe they were just in the wrong place at the wrong time. Nobody could have anticipated that these two cartels were going to be in a war. Reporter: Mexican authorities say the gunmen fired more than 200 rounds at the women and children. The family part of a Mormon community that had been living in the border region for the three mothers driving in separate vehicles caravanning to stay safe. Some of them preparing for an upcoming wedding. They never arrived to their destination and family members were too scared to drive over the road to find them with all this going on. There was gunshots going on after the vehicle had burned. Reporter: Three mothers and six children including twin infants shot and killed. Family members sharing these photos with ABC news. This is ronita Miller holding her twin babies all three killed in the attack. At one point one of the mothers got out of her vehicle with her hands up to show they were families. The gunman shot her point blank in the chest. President trump reacting to the horrific news tweeting, if Mexico needs or requests help in cleaning out these monster, the United States stands ready, willing and able to get involved and do the job quickly and effectively. Reporter: But Mexico's president saying their country will handle this alone, vowing justice. Aliza stell said her cousin Christine Langford killed in the attack may have been trying to save her 7-month-old baby faith. The mother tried to put the child like on the floor under the seat in some way to save her life but baby faith is her name, she survived. Reporter: So many relatives calling 13-year-old Devin Blake Langford a hero. They say he saved several of his siblings who had been shot hiding them in some bushes as he walked 14 miles to get help amid what they describe as an all out narco war. He saw the cartel shooting. There were like 60 people shooting at them from all over the mountains around and the little kid decided to get the kids away from where they were shooting and go into the bushes. That was courageous. Reporter: Five taken out by helicopter now being treated in Tucson, Arizona. And, again, we cannot stress enough how much that little boy is a hero. He saved all those children. We also want to mention despite Mexico going at this alone they are sharing information with the FBI. But this is a very remote location. Outside from where we are it gets even more dangerous but Mexican officials are calling this what it is, an atrocity. It certainly is. Certainly it, Tom. Thank you.
This transcript has been automatically generated and may not be 100% accurate.