Las Vegas shooter may have been planning to attack targets in Chicago and Boston

In August, shooter Stephen Paddock booked rooms at Chicago's Blackstone Hotel for the same dates as the Lollapalooza festival across the street in Grant Park, but he never checked into the hotel.
4:01 | 10/05/17

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Transcript for Las Vegas shooter may have been planning to attack targets in Chicago and Boston
Good evening and it's great to have you with us here on a Thursday night. And we begin with major new developments in the Las Vegas massacre we are learning the killer may have scouted other potential targets in Chicago and in boss tone. And the dramatic new video from that night. Run, keep your head down. Go. Keep your head down. Go. You can hear the officers telling the thousands to run for their lives, helping the victims who had been shot and who had fallen. And tonight, our team flying beside the hotel and over the massive crime scene where the FBI is still carefully combing through the evidence. ABC's senior national correspondent Matt Gutman leading us off again tonight. Reporter: We boarded a helicopter here in Las Vegas for the first look tonight into Stephen paddock's sniper's nest. High above the Las Vegas strip at the gilded facade of the mandalay bay hotel. Inside one shattered window, pillows stacked high on a stripped bed. The other window, partially blocked by plywood. But inside, investigators carefully dissecting the scene. Down below, you can see FBI agents picking through every single piece of debris down there on the fairgrounds floor. They don't want to miss anything, a single bullet fragment or a single piece of evidence. This is the aftermath. But tonight, new video gives new insight into the chaos on the ground. Get down! Reporter: That gunfire triggering hysteria, confusion. Shockingly, people seem unable to process what's happening. Run, those are shots! Run! Don't walk! Reporter: Police officers yelling at them that they're under attack. Everybody go! Reporter: Right there, there's a woman on the ground, as the crowd runs past her. Let's go! Get up, run. Let's go, get up. Get up on your feet. Let's go, I'm with you. On your feet. Thank you. Reporter: That video shot by ray page, who went to get his truck, parked nearby, driving it back into the kill zone, turning it into a makeshift ambulance. Right here, come in here. Reporter: The wounded loaded in, one after another. Get in the truck, get in the truck. Do we have any other wounded people we can take? Not right now. Reporter: Ray then jumps behind the wheel, drives them back down the strip to paramedics. Ingot five wounded. One in the chest here. Someone help, please, please. I'm bleeding so much. Reporter: Today, from high above, evidence of a massacre still frozen in time. It doesn't look so much like there was a concert there, but that a tornado swept through there. Those overturned lawn chairs, we've seen strollers, walkers there. Evidence of just the absolute chaos. And tonight, we are learning that Stephen paddock may have scouted other targets as far away as Boston and Chicago. According to sources briefed on the investigation, he booked rooms at Chicago's Blackstone hotel in August, the same dates as the lollapalooza festival right across the street in grant park. About 100,000 people attended each day. But paddock never checked in. Law enforcement sources also tell us his phone shows a Google search for "Hotels around Fenway park" in Boston. That ballpark's capacity? Nearly 38,000 people. But no evidence he traveled to Boston, either. Instead, he stayed close to home, holing up in one of the casinos he knew so well, looking down on that helpless crowd. So, let's get to Matt Gutman live with us again tonight. Matt, not you're learning, there might be someone else authorities want to talk to? Reporter: That's right, David. Investigators say that paddock was seen with a mystery woman in his last days. Now, she was not his girlfriend. They're trying to find out who she is and what she knows. Also, given the arsenal that he amassed, along with explosive materials and the fact that he may have had an escape plan, they're now saying that they cannot rule out that he had an accomplice. David? Matt Gutman leading us off. Matt, thank you.

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

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