National Park Slaying: Rock Climber Charged With Killing Friend

David DiPaolo claims self-defense in the death of his longtime mentor Geoffrey Farrar.
3:00 | 01/16/14

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Transcript for National Park Slaying: Rock Climber Charged With Killing Friend
mysterious death at a very popular hiking spot right outside washington, d.C. A young rock climber is charged with killing the friend and mentor he had known since he was a little boy. He's claiming self-defense. Abc's reena ninan is here with the latest. Good morning, reena. Reporter: Good morning, the two men were reportedly friends and those who knew them tell us they are surprised the man found dead geoffrey farrar was said to have mentored for two decades a 31-year-old now accused of killing him. Geoffrey farrar loved scaling these rocks at maryland's carderock park so much he even earned a nickname. People would call him carderock geoff. Reporter: Little did he know he would spend his final moments there. The 69-year-old found dead at the rock's base after climbing with three friends including the man he mentored for 20 years, david DiPaolo. At first many thought it was an accident. We had an operating on the assumption that it was an accident just doing something that he loved. Reporter: But now police say it was manslaughter. According authorities farrar and DiPAOLO WERE SEEN ARGUING RIGHT Before the climb. Their two companions said they went to the top of the rock face but looking over the edge they see no one. When they walk to the bottom THEY SEE 31-YEAR-old DiPaolo running up the trail and farrar lying nearby next to a wooden beam bleeding from the head. His injuries were not consistent with the fall but more in line with a blow from a claw hammer found nearby on the ground. I can't imagine anyone needing to use a claw hammer for any rock climbing purpose out here. Reporter: Dipaolo fled the scene. More than a week later police say he admitted he did hit his friend farrar with a climbing tool but claims it was in self-defense. According to court documents, he says farrar tried to choke him fearing he was losing consciousness he whacked farrar in the head. The court documents say he later told police, I'm sorry this happened. I didn't want it to happen. I didn't know it was going to happen. AUTHORITIES SAY david DiPaolo was arrested near glen falls, new york, he's agreed to return to maryland to stand trial.

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

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