From: People--When Marine Sergeant Cody Leifheit awakened to screams from outside his apartment at 2 a.m., the 28-year-old at first thought the sound was from revelers leaving a bar. Then a hysterical voice screamed: "He's dying!"Leifheit, who arrived in town only a week earlier to start his job as a Marine Corps recruiter in Lewiston, Idaho, jumped from bed and ran outside. There, a group of young people stood gaping at a horrific site: A man hanging by the neck from a rope, suspended from a tree branch some 25 feet above the ground.The 19-year-old man, who asked that PEOPLE refer to him only by his first name, Tristan, had been lounging with friends inside an elaborate series of hammocks strung from trees. While in his hammock in the early morning hours of June 7, Tristan repeated to friends that he wanted to jump to his death from a tree. The friends thought that Tristan, who has sole custody of his 14-year-old brother, Dartanian, was joking. Suddenly, up in the trees, Tristan stopped talking.Now, confronted with the stark reality that Tristan was serious and might die, his friends were shocked and in hysterics.Fortunately for Tristan, the screaming brought capable help in the form of Cody Leifheit.The sergeant arrived on scene and instantly took charge. He asked the friends to stop screaming and to sit on a nearby porch."I picked a kid, pointed at him, and said, 'You. Call paramedics. Now,' " Leifheit tells PEOPLE. "I asked for a knife. No one had one."But Leifheit had one at home.Racing desperately against time, the former standout high school wrestler and football player retrieved a knife from his apartment and returned to scale the tree."The sergeant was like Hercules coming up the tree," says 20-year-old Austin Tow, who had climbed up to help Tristan, his roommate. "He just strong-armed his way up."From his perch atop a branch, Tow had been trying to figure out what to do to save Tristan."If I cut my friend down, he could die from the fall. If I left him there, he would die from hanging,” he said.Leifheit instantly took charge."When the sergeant arrived, he said, 'Hey, I'm a Marine, and I'm here to help your friend,' " Tow says. "I was so happy to see him."Leifheit told Tow: "I got him.""I lifted him up and put him in my lap," Leifheit says.But the rescue was far from over. To his horror, Leifheit found that Tristan had no pulse."I used the tree as a backboard and started chest compressions," Leifheit says.Tristan had been without air for so long that his body struggled to respond."He bottomed out on me a few times," Leifheit says, "but he revived."Rescue crews arrived to relieve Leifheit. A paramedic propped a ladder against the tree and climbed up to the branch.The paramedic found no pulse. He adjudged Tristan dead."I said, 'No way!' " Leifheit says. "I went back to work. His heart started beating again."Leifheit and Tow carefully draped Tristan over the paramedic's shoulder. The paramedic then carried Tristan down the ladder to a waiting ambulance. Tristan was whisked to a hospital, where he was placed in a medically induced coma.Forty-eight hours later, Tristan awakened to find his greatly relieved 14-year-old brother and legal dependent, Dartanian, sitting watch at his hospital bedside."We had a long talk about what happened," Dartanian tells PEOPLE. "It knocked some sense into him. I'm glad he's better.""I wasn't there, mentally," Tristan says of that night. "This has been a wake-up. I'm glad the Marine was there and did what he did.""He didn't have to help," Dartanian says of Leifheit. "When I saw him, I just gave him a big hug.""It was so honorable and so respectable," says Tow. "The sergeant is a hero." "This is just me being human," Leifheit says. "You would have done the same thing. If you're physically capable of doing something to save someone, you do it. What I did was not a heroic act." Dartanian believes otherwise. "He saved my brother. If my brother was gone, I don't know where I'd be. I don't know what would happen to me. I don't know what I'd do without him."