Authorities search for clues in deadly school shooting

ABC News' Tom Llamas reports from the home of suspect Nikolas Cruz in Parkland, Florida, with the latest details on the high school shooting that left 17 people dead.
4:07 | 02/15/18

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Transcript for Authorities search for clues in deadly school shooting
We're also learning more about the shooter in this horrific massacre, 19-year-old Nikolas Cruz, a former student at the school expelled for disciplinary reasons and had been identified as a potential threat. Our chief national correspondent Tom llamas is also there in Florida. He is outside the shooter's home about new details about his past. Good morning, Tom. Reporter: Robin, good morning to you. The police presence just behind me is getting larger by the minute. Both local police and the FBI are now here just around that corner in parkland, Florida, right here where the alleged shooter lived with a friend and the friend's family. In multiple the interviews with the alleged shooter's relative, classmates and former friends were getting a profile of a teenager obsessed with guns and who at least once before made a threat that he was going to shoot up his school and just last night a relative of the alleged killer telling us that he was adopted but his adoptive father died early on in his-and just months ago, robin, his adoptive mother died a painful and sudden death when she got the flu. Several students who spoke with ABC news say it was no secret the teenager you see in this photo was dangerous and even threatened to kill. He carried multiple guns. Reporter: Police describe Cruz Kris as armed for a war when he allegedly stormed this south Florida high school. Senator bill Nelson says the FBI informed him the alleged gunman had a gas mask and smoke grenades along with his assault rifle. He had countless magazines, multiple magazines and at this point we believe he had one ar-15 rife. I don't know if he had a second one. Reporter: The 19-year-old seen here being taken down and handcuffed by law enforcement was wearing an rotc maroon shirt and combat boots. Others paint him as troubled. About a year ago I saw him upset in the morning and I was like what up. He was like, I swear to god I'll shoot up the school and I said, Yo, watch what you're saying around me. Reporter: That student tells us he warned school officials. Cruz was eventually expelled from Marjory Stoneman Douglas high school. He got in a fight with this one kid, and then from what I know, he was allowed to bring his backpack because they found bullet casings in it. Reporter: Former classmate Joshua Charles said he tried to sell him weapons. He offered to sell my knives. I just thought he was one of those kids who he likes to have fun with objects like that. Reporter: Overnight the FBI searching for clues in the parkland, Florida, home where he last lived and the focus this morning from investigators, any hint of a motive on social media. We've already began to dissect his websites and the things that social media that he was on and some of the things have come to mind are very, very disturbing. Reporter: Experts tell us judging from the shooter's age his social media profile and relationships with other teens will likely turn up major clues. I guarantee you there is information out there that he was going to do. That, you know, when he acquired the firearms if he did or got them from home, the things he may have said on social media. Reporter: Students at Stoneman Douglas high school say they point to pages that belong to him. He is seen holding a pistol. Anoth another shows an arsenal of weapons. They're now being looked at. I think everyone in the school had it in the back of their mind if anyone was going to do it it would most likely be him. Reporter: To you there was a social media user on YouTube who was posting comments with the same name as the alleged shooter Nikolas Cruz saying he wanted to kill different groups of people. Now this morning buzzfeed is reporting that one YouTube user noticed this and alerted the FBI because one of the posts from the led shooter said he'll be a professional school shooter. Now, the FBI followed up but it's unclear if it ever led back to Cruz. Robin and Michael. They're still looking into that. All right, thank you very much, Tom. I'm really struck -- going back to George -- struck by both young people you spoke to, especially the young man who said we should not -- we can't get used to this. We can't become numb to these types of incidents. And, robin, we say that again and again and again but no one could say it more powerfully than that young man in the middle of it at that moment. We've seen so many of these. 18 this year, more than -- almost 300 since sandy hook. Think about that. Almost 300 school shootings since sandy hook and now here in parkland, Florida, in one of the safest cities in America. One of the trending hashtags yesterday, enough is enough. We'll get back to you.

This transcript has been automatically generated and may not be 100% accurate.

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