Transcript for What we know about Vegas mass shooting suspect Stephen Paddock
Paddock is solely responsible for this heinous act. Reporter: Stephen paddock with no criminal record is now allegedly the man behind the deadliest mass shooting in American history. From mandalay bay he unleashed a torrent of bullets into a crowd of a music festival 1100 feet away. Listen. The sound different from any we've heard from all other recent mass shootings because this time a rifle functioning like a machine gun was used. The individual is described as a lone wolf. I don't know how it could have been prevented. Reporter: As the death toll has continued to rise, investigators rush to track down anything about the shooter. We're trying to understand what's wrong, what happened. We're still just completely befuddled. Reporter: Eric paddock, the shooter's brother says he has no clue what led his brother on this murderous rampage. Remembering him as a man who grew up without conviction. Steve had nothing to do with any political organization, religious organization, no white supremacist, nothing. As far as I know. Reporter: And the FBI says there's no connection to any overseas terror group despoit a claim today by ISIS. We have determined at this point no connection with an international terrorist group. Reporter: While he enjoyed gambling, his brother said he didn't have a problem and had recently won a $40,000 jackpot. He was a wealthy guy and he liked to play video poker. He went on cruises. He sent his mother cookies. Reporter: But in recent months, paddock's financial activities had become abnormal, sending tense of thousands of dollars to someone in the Philippines, authorities say his girlfriend Marilou Danley is right now. Officials are hoping Danley who once worked as a casino hostess for high end players may provide insight. Earlier today authorities descended on the two homes paddock owned in hopes of finding a lead. One in Reno. At the other in Mesquite they used a robot to take down the garage door. Once inside they found 19 guns. His family says he's a licensed gun owner before this incident. Yes, he had a couple of guns. He did not own machine guns that I knew of. Something incredibly wrong happened to my brother. Reporter: What we know now was the murderous attack was planned. Paddock had built up a massive arsenal inside the hotel room. We got shots fired. Sounded like an automatic firearm. Reporter: According to authorities he had at least 23 rifles and handguns, one of them an assault rifle modified to fire automatically. Some of the weapons were high powered, capable of slicing through police body armor. This is a classic wmd. This is a weapon and a man of mass destruction. Reporter: According to authorities, many of the guns were bought legally. The mesquite-based gun shop guns & guitars confirmed that paddock had legally bought some guns from their shop. All necessary background checks were followed. He never gave any indication or reason to believe he was unstable or unfit at any time. The general manager said in a statement. We do not yet know if these guns were used in the attack. Nevada has some of the least restrictive gun laws in the country. There's no limit on the number of firearms one person can possess. And semiautomatic weapons are legal to purchase. Their capability far exsides that of a handgun. When adapted the potential to be even deadlier. As seen in this YouTube video. It's a significant game changer in the way we respond to active shooter. Minutes are not quick enough. Reporter: Tonight the deadly power one man was able to wield leaving us all to ask the question, why did it happen again? Former New York City police commissioner and ABC news contributor ray Kelly is with us tonight. Commissioner, tonight what are investigators looking for, do you think? Why? That's the big question. Why did this individual apparently ordinary person, no kr criminal record, why did he do this? The biggest mass shooting in Thi the history of our country. I'm sure there are signs that people should have seen. Talk about that. What kind of signs do you think people missed? We don't know what the signs are. They will be hopefully identified during the investigation. But suddenly violent behavior or threats to do something like this. These are the types of things that we've seen in investigations of this nature when they go forward. People in your business are students. You're always learning from yes. What will law enforcement take from this to apply in the future? I think we'll see more anti-sniper capacity put in place by police departments throughout the country. You have to be a fairly good sized police department to do that because most don't have the resources to do it. The New York City police department has been doing it for years when you have major gatherings. But we're blessed with the numbers to do it. But there's no easy way from the ground of getting someone who is shooting from 32 stories up. Commissioner ray Kelly, thank you very much. Thank you.
This transcript has been automatically generated and may not be 100% accurate.