What we know about deadly shooting at Florida high school

The suspect's name is Nikolas Cruz, 19, according to multiple law enforcement sources.
7:18 | 02/15/18

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Transcript for What we know about deadly shooting at Florida high school
running in the building. Today the unthinkable happened again. I'm sick to my stomach. Unfolding this time at Marjory Stoneman Douglas high school in parkland, Florida. I jus heard gun shots. This is a terrible day. For United States. Events like this continue to happen. So American law enforcement and teachers are getting to be experts in responding to deadly incidents like this. Minutes and seconds matter because so much damage can be done by the type of weapons that are available in our country. Semi automatic high-power rifle. The capacity to hold more bullet in the magazines creates this dynamic of multiple frtragedies. Today's ranks among the top five deadliest to date. Now they're doing fire drills. I'm going to kill everybody nobody's getting out. Some go as far as covering student in fake blood all in an effort to make the drills more realistic. Attention. This is a drill. We need to lock down. In 2014 we embedded at sky view academy in Colorado as they went through the standard lock down drill. Please go behind my desk. The teacher locks the door and pulls the shade. Everyone's told to keep quiet. It's kind of squary. Yeah. The kids huddle quietly. Do know why they do this did drill. To practice in case anyone comes here. Do you worry this scares students. We do but we practice enough that we hope that students are and staff is getting used to the idea. We have to. How long do these go for. Five minutes is longest we've had. Teacher Holley carpenter supported these drills she's a graduate of columbine high school. When you look at those kids are you always thinking someone could come take their lives. No I look at those kids and think how great they are, how lucky I am to teach them, and I think by wonder what they're going to be like when they grow up. That day changed her life and is why she take these drills very personally. I always get a lump in my throat it's not about flash backs of columbine it's about the thought of anyone even wanting to hurt the kids. Sky view academy doesn't just do the basic lock down drill while we were there the teachers were getting a new method of training. Nobody's getting out. Teaching everyone not just to duck but to respond. Active shooter training is the new Normal and because these incidents are repeating themselves, escalating and we're learning lessons from failures in the past. How did you feel? Lots of adrenaline. Former swat team member has responded to active shootings for real. This open. What's that mean? He's teaching them how to recognize when shooter is reloading his gun. He's out. Right. And teaching defense tactics. There we go. Good. Good. How to take down a shooter. First responders do too back in 2016 night line embedded with the Douglas county sheriff's department. In a scenario this time more complicated. Shots fired. Hostages strapped to explosives and multiple schools on alert. Deputy and first responders race down the stairs and hallways not knowing how many gunmen there are. Just as things are heating up at the high school another call sends deputies to a different call up the street. Possible shooter at the middle school. Two deputies head in alone. No time to wait for back up. Inside helpless victim. One student chained to a bomb. These cops know their first priority is to eliminate the active shooter. In this scenario hold up in a first floor bathroom. Drills such as this are no doubt good practice for the professionals. But is it fair to expect teachers and students to put themselves in harm's way. Is that teacher or student really going to be able to take down 200 pound gunman. Let's find out. Joe is about 220. Pick out anyone in the crowd and see. Let's do it. So we got Holley carpenter in her columbine sweat shirt to do it again. This time the guy's going to fight back. This time the gunman resisting her effort to disarm him. She's glad to have strategy she can use if her life is on the line. How's that feel? Really good. This active shooter drill ends with a different version, this time everyone arms themselves with a tennis ball but in real life might well be a airy, this time it's the active shooter whose the sitting ck. Would this works if the bullets were real or if this were a class full of kids, hard to know. But unfortunately with every incident like today in parkland more and more communities figure better safe than sorry. Our thanks to you David we'll

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

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