Transcript for Arizona college party ends with a deadly shooting: Part 1
Reporter: Its motto is, "The world looks different from here." And it does. Northern Arizona university sits 7,000 feet in the air. Surrounded by the snow-capped San Francisco peaks and a ponderosa pine forest here in flagstaff, Arizona. Plenty of wide open spaces, for any kid looking to strike out on his own. There's so much to do. You have sedona and the grand canyon. The mountains. Flagstaff is really homey if you will. It's got a comfortable, welcoming feel to it. Nau, same thing. I mean, flagstaff and Nau, they're not separate. It's just all one big community. Nau is one of three state schools in Arizona. It's got about 20,000 students, but it has a very close-knit feel among the students on campus. Reporter: One of those students who arrives as a freshman in the fall of 2013 is 18-year-old Colin brough. Here to study business. And how did he come to choose Nau? He applied to csu, Boulder and Nau. And Nau was the furthest away so that's why he picked that one. Because he wanted to be away from home, and just wanted to be on his own. Independent. Reporter: Claudia and Doug drop him off, 10 1/2 hours away from their Colorado home. Sure he will be safe. Looking around this campus, can you tell why he liked it so much? Well it's a great community. It's a beautiful community. Reporter: At first, it seems Colin is suffering from the all-too familiar fall freshman blues. He would always kid me, "I'm not going to be homesick. I can't wait to go." Two months later, "I think I made a mistake. I want to come home." Reporter: But the jitters start to fade once Colin begins making friends. Like fellow freshman Nick piring. We became random roommates freshman year in the dorms. I met his family the first day, just became really close right off the bat. Reporter: Would you say he's your best friend? One of my best friends, for sure. We ended up rushing the fraternity second semester. Reporter: Kyle Zientek also meets Colin at that fraternity. Well, you're smiling, you're grinning, so. Just thinking about just the kid's like heart, honestly. The smirk that he always had too just was, I don't know. That kid had something just about him. Reporter: The boys join the delta chi fraternity at Nau. A school where Greek life is big on campus. The people, the programs and of course the parties. Parties like this one, shot by an Nau student. That's the part that worries Colin's parents. What was your impression? I kept thinking, like "Animal house." ??? 'cause that's all I really knew. Reporter: That paints a picture. I wasn't happy about it. But I told him he could make those decisions. Reporter: And that was your whole philosophy bringing up the kids, right? When you're in my house I'm going to take care of you, you're going to be safe, but when you go off to college. You're going to explore, make choices that you're going to live by. Reporter: By sophomore year Colin and his friend Nick move off-campus to this apartment complex known as "The courtyard." It's a popular spot for delta chi, housing several of their fraternity brothers and is conveniently located just across the street from Nau. We had the whole little courtyard so we could go out there, maybe, you know, just get together, play some beer games or something. It had sort of a reputation at the time for being a place to party and hang out. Police were often visiting the courtyard, getting noise complaints, getting complaints of students drinking. Reporter: Were you concerned that Colin would go off to college and start just partying his face off? I was always concerned about that and of course I didn't like it. But I knew in the end he would get it out. Reporter: But before he would get the opportunity to do that, tragedy strikes on campus. Nau has been in existence for 118 years, and for 116 of those years there had never been a shooting on campus. That changed on the night of @ October 9th, 2015. Reporter: The night starts out like so many others, with a party at the courtyard. What are you guys doing that night? We're just hanging out. Just a couple people drinking, it's Thursday night. It wasn't anything crazy. Reporter: Do you guys even know what started everything? No, no, I don't know what happened and how it started. Reporter: Around 1:00 A.M. Nick and Kyle along with several other people at the party say they hear what sounds like an argument going on in front of the courtyard. It wasn't a memorable night. Reporter: Zach volpo and Nick pletke are also delta chi brothers who are at the party that night. There's a verbal confrontation going on on the street. All of the sudden I see the group move into the parking lot, and then that's when I saw the flashlight flick on. Reporter: Do you remember ever seeing the gun? I remember seeing a light. I thought it was, security guard or a cop or something. Had no idea. I look down for a second, either at and all of the sudden I hear three, four loud, really, really loud bangs. I thought it was fireworks or something. Reporter: Zach runs across the street into the Nau parking lot and he's horrified. Colin brough and Nick piring are down. Both of them bleeding on the ground. Each of them shot twice. I was in so much shock, I had no idea. And so I saw a puddle of blood next to me. The only person I didn't recognize was the one standing, and I realized that he was the gunman. Immediately turned around, book it back, try to find some cover. I saw this blinding light, it kind of clicked with me that something's not right. Reporter: The shooter fires off several more rounds. This time hitting delta chi brother Nick prato and Kyle Zientek. How do you get shot in the back? I turned around when I saw that light. Next thing I know, like, on the ground and it's just, it's like all numb. Reporter: When we come back, how did a college party turn into a war zone? As police arrive, they confront the teenage shooter. Body cameras capturing all the action. Can I call my mom? Reporter: And you'll be shocked when you learn who that shooter is.
This transcript has been automatically generated and may not be 100% accurate.