Transcript for College student shot dead in Brooklyn neighborhood after night of partying: Part 1
I'm elizeth vargas ahis is "20/20 here's "nightline"'s juju Chang. Good morning. Are youready? I am.rikers, here we go. Rikers here we come. What a cheace to visit huh? Reporter: Doreen Quinn Giuliano has becl too miliar with one of the country's most dangerousnd notorious jails. It's out of control. It's very violbetween inmates and E guards. You don't know who to trust. Reporter: Every week, she makes the hour-long drive from her H in brolyn to rikers nd to see hen John. John doesn't belong here. WRE does he Bel Home. Reporter: But in 2005, a juryjury convicted John guica O order, sending him away for 25 years to life. Does it ever cross your mind that maybe John did have something to do with it? No. I'm sure he did not. How can you be 100% re? Well, facts. Just follow the facts. T's part ofthat's sympathetic to Doreen Giuliano, analmost admthe fact that she stood by him to this pot. But John Gius not the victim but John guica is not the victim in this case. It's mark fisher. Reporter:was columb day weekend, 2003. 19-year old Coe student fisher is taking a long weekend a eak from theooks and classes. Wanting to blow off some STE, he heads to the big apple to explore the hopping bar sce on nhattan's upper east side. It had to be tremen exciting for a guy from suburban New Jersey. He's going to big city for the first time, and there are going to be me girls the he knows from schl. Reporter: That school Fairfield university W fish, a sophomore, is an accountant. Mark fisher was every parent'sream. A big strapping, good-looking student-ete, prom Ng in his high school, a phenomenal football player. Reporter: Bn that night, mark fisher has no interest in running defensive plor crunching numbers. He's just looking to have a good me. Mark runs into a girl that he goes thool with. She brings a lot of her friends with her. Reporter: There's one pretty blonde he't his eye on. They bond over a couple slices of pepperoni. He S following her wherever she went that night. Reporter: But whastarted as an innocent GHT on the town, soon Tak different T after the twose meets Tommy Saleh and his buddies. A bunch of us went to these bars on like tpper east side. A bunch of guys. Aunch of guys, um. Cruising for chicks. Yea Reporter: "Cruising for chicks" G with him that night his wingman from high scol, John guica. Best friend Yeah. Hang out every day, um, weekends. Rter: They try and fail to score some drinks. Fake id's didn't make it. No. Some members of the group were unable to get into th bars Reporter: So, 20-year old eporter: S 20-year-old John guica comes wit a plan. He says, "My parents are away for the weekend. Y don't we gto my house and have a party?" This was an impromptu party, this was nothing THAs planned, twas something that just happened. Repor their journey that night will take them from dy bars of nerk's upper side -across the fabled Brooklyn bridge -- where mark fisher has no idea what he about et himself into. Why wasdecided to go to John giuca's house? His mom was away. He had a big house. It was like easy choice So it was a little bit like, the cat's away, the mice Wil play? Yeah. I was in florid weekend vacation with my husband. And John decided to throw an impromptu Y. I mean, there was a few kids at got stranded inanhattan and had no pce to go. Reporte one of those stranded kids is mark fisher who now is not only end -- he's hammered. According do -- toommy Saleh, er is intoxicated, strapped for cash and ho way to get back home to New Jersey. Us. So this kid you just pretty much out of it. Eah. Didn've money. Let's just take him home and let him sleep it off? Eah, I'm assuming he was friends one of thels or soing like that. And he figured he'll brin them here to my house, get some ers, and be -- young adults, you teenagers. Drinking. Ding. I'm sure they were smoking also. Smoking weed? Yes. And yet, that impromptu par turned into, perhaone of the biggest mistakes of his life. Oh, Y yeah. Absolutely. Reporter:oreen says one those mistakes her son's decision to invite neighborhood "Bad apple," Antonio Russo known for his long dres and a penchant picking fight So tell me about Antonio Russo. He was a bit of a wild child. Was younger than all the other boys. He was more of a street kid, he didn't have the support system at home tjohn giuca and maf John's other friends had. He's known to be a marijuana dealer. Reporter: Antonio Russo, aka tweed, is said to supply the weed. At one point after mark had bet this hour about an hour or so it's believed that John giuca basally accused him of being mooch. He was drinking beer, he S smoking their pot. He wasn't bucking up. Reporter: According to witnesses, guica though was time R the mooching mark fisher to pay up. Shortly after 5:00 A.M., maisher wentan atm machine and purchased a six-pack of beer. Eporter: Whappens over the next hour, depen on whom you talk to party. T somehow, in those early mornhours, marfisher the handsome college student out for a nighon the town stumbles aw from the party. Two blocks away to Argyle road, and winds up dead. I can tell you that ou detectives, when they arrived ate ene, they found a male white prone obviously the victim everal gun shots. There was some trauma to his face. Reporter: The strapping 6'3" 205-pound er football pl from New Jersey is fnd shot fivees in the back lying on a blanket from giuca's home. When you hears a kid from W Jersey right away, you're saying, "What's wrong here, and how did this person end up here?" His some sort of deal gone bad, is this sort of a domestic issue?
This transcript has been automatically generated and may not be 100% accurate.