Dave DiPaolo, who struggled with drugs and mental illness, pleaded guilty to the 2013 slaying of his former climbing mentor, Geoff Farrar, at Carderock in Maryland. DiPaolo is set to be sentenced on July 18. (Warren County (Va.) Sheriff’s Office)

Geoff Farrar was beaten to death with a hammer on Dec. 28, 2013, at Carderock, which is a series of cliffs frequented by rock climbers along the Maryland side of the Potomac River. Farrar was a climber. Some people called him Carderock Geoff because he was a constant presence at the rocks, like the sycamores and brambles growing in the bottoms.

He was found bleeding badly from head wounds at the base of a route called Cripple’s Traverse. An ambulance from Montgomery County showed up first. Next came a pair of county rescue boats. Finally, a helicopter from the U.S. Park Police arrived on the scene. It hovered close to the river. The pilot rocked the Bell 412 to swing a rope to shore, and emergency workers were able to clip in the stretcher that now held Farrar. The helicopter lifted slowly, carefully hauled Farrar inside, then flew him to Suburban Hospital in Bethesda. His injuries were too severe, and he died a few hours later. He was 69.

The man who killed Farrar and who will be sentenced to prison this month for his death was also a climber, a younger man named Dave DiPaolo, who was then 31. He, too, frequented Carderock, and DiPaolo and Farrar made for an odd couple. Their relationship was complicated. It had started more than 15 years earlier and originally been shaped around something approaching a father-son framework. But that structure no longer quite fit as the men grew older and DiPaolo struggled with drug abuse, mental illness and a generally unstable life.

Carderock is part of the Chesapeake & Ohio Canal National Historical Park and an unlikely location for a homicide. It is a beautiful and serene place, an open-air cathedral for religions yet unnamed. Although the cliffs rarely rise above 40 feet, they seem taller, looming overhead and creating a shelter from the wider world. Washington is just a few miles to the east, but it’s possible at Carderock to lose oneself in the nature of the rock and to believe that the strife of the city and the problems of everyday life can’t travel upstream.

In the immediate days after Farrar’s death, there was confusion about what happened. The first reports said Farrar had died from a fall, and that led to some online sniping that criticized him for taking unnecessary risks by climbing too high without a rope. Farrar’s paid obituary only added to the uncertainty; it said he had been killed in a rock-climbing accident.

After DiPaolo was arrested Jan. 8, 2014, and charged with voluntary manslaughter, the pendulum swung in another direction. People tried to make sense of a harsher tragedy. Many climbers in the tightly knit community of regulars at Carderock knew both DiPaolo and Farrar, knew how close they had been and knew that something must have gone terribly wrong. It wasn’t just that one man was dead and another in jail. Or that violence had visited their sanctuary along the river. It was something more basic. “We were part of a tribe,” one climber said. And on that warm December afternoon, on the footpath beneath the cliffs, the tribe had been attacked by one of its own.

Geoff Farrar had a passion for climbing and was once a mentor to the man who killed him. (Courtesy of Dave Rockwell)

Even Geoff Farrar’s closest friends said he could be difficult. He liked to needle people and was a man of strong opinions on just about everything. But there were plenty of climbers at Carderock who embraced Farrar and his antics because he was generous, intelligent and entertaining and because he really understood how to climb.

“The thing about Geoff was he was a little bit abrasive, but he was a very likable person, actually, and once you really got to know him, you really liked him,” said Todd Bradley, who learned to climb at Carderock. Farrar taught him the physical aspects of climbing — footwork and balance — as well as the mental component, that climbing was as much about problem-solving as about strength.

Farrar could be counted on to be at Carderock most every afternoon if the weather was good. That had been the case for more than 30 years. He didn’t work, hadn’t worked for years. At one time, he repaired microfilm cameras for the federal government and banks. He sometimes told people he had worked for the Central Intelligence Agency, but nobody really believed him. Some friends knew he owned a lot of guns; others weren’t supposed to know.

He was married, but his wife, Linda Proudfoot, spent most of her time in the small town of Philippi, W.Va., four hours west of Washington, and was generally not part of the Carderock scene. (She didn’t return telephone calls or answer a letter seeking comment.) Farrar preferred to stay at the house they owned in the Bellevue Forest section of Arlington, Va., where he was known as a grumpy neighbor.

It was eight miles from his house to Carderock, but none of the friends I talked to had ever been there.

At this stage of his life, Farrar was primarily a boulderer. He was tall and gangly, deceptively agile for his frame. He liked to work shorter climbs, gradually making a route harder by eliminating obvious holds, and he was always providing what climbers call “beta,” the not always obvious information on how best to attack a challenging section.

“He would define a problem to its most classic and hardest steps,” said Dave Rockwell, one of the Carderock regulars. Farrar was the community’s hub, in his own way an idiosyncratic boulder. The cliffs were a clubhouse, and it was the sort of place where the members had nicknames. Rockwell was known as Old Dave, to distinguish him from Young Dave, who was not the same as Little Dave.

Little Dave was DiPaolo, and he began climbing at Carderock when he was a teenager. His father, Vincent, was also a climber, and he encouraged the relationship between Farrar and his son, as a way to learn about climbing and about life. “David was an incredible climber,” said Vincent DiPaolo. He was strong and lithe and fearless, routinely climbing the hardest route at Carderock, which is named Silver Spot and is a slightly undulating vertical sheet of rock. Sometimes, he would climb it without a rope.

Farrar had worked with lots of young climbers. He would teach them rope work, how to communicate properly on a climb, how to set an anchor and how to smear a rock-climbing shoe against a button-size nubbin, then stand on the hold and reach for the next one.

Despite DiPaolo’s prowess as a climber, his life outside the rocks was difficult. From the time he was a teenager, he suffered from mental illness; according to court records, he was hospitalized on at least four occasions between 1999 and 2003. He was also using drugs, often heroin, cycling through addiction and rehab. As a young adult, he lived in Canada for a while, then moved back in with his father in Bristow, Va., in Prince William County. In recent years, his closest companion was a dog named Caesar that he had rescued. It died last year while DiPaolo was in custody. The two could often be seen at Carderock together, DiPaolo with his bushy ponytail and knit cap and little Caesar, equally shaggy, happy in the moment.

“If you wanted a portrayal of a surfer, stoner pothead, that was Dave,” said Marc Stinebaugh, a friend to both men.

Court records detail DiPaolo’s struggle with drugs, including heroin. Like DiPaolo, Stinebaugh had come to the cliffs as a teenager and also found a climbing mentor in Farrar.

Farrar’s habit of picking on people could have a sharp edge. Vincent DiPaolo said that over time Farrar became jealous because the student had surpassed the teacher. He would push DiPaolo, trying to provoke him or — if that failed — get his father to bring him in line. “Many times he would say to me, you should give your son a good whipping,” said Vincent DiPaolo.

Most of the climbing that takes place at Carderock is top-roping. The climbers secure an anchor at the top of the cliffs, usually by placing webbing around a tree or a rock. The first climber is tied into the rope, which goes up to the top and then through a carabiner, which is a large clip attached to the webbing, before heading back down to the second climber. He uses a friction device to hold the rope fast and prevent the first climber from falling if he comes off the rock.

The techniques are not difficult, but they require communication and concentration. It can be a bonding experience built on trust, what one climber called “the comradeship of the rope.”

Two years before Farrar was killed, DiPaolo had dropped a climber during a descent at Seneca Rocks in West Virginia. The rope was shorter than he realized, and it hadn’t been properly knotted at the end.

The result was that DiPaolo ran out of rope, and by the time he realized this mistake, the rope had slipped through his hands and the other climber fell 40 feet, breaking his wrist. It became another blemish on DiPaolo’s reputation, further marking him as unreliable.

Farrar and DiPaolo got into a heated argument in the parking lot at Carderock on that December afternoon in late 2013. A climber named John Gregory was a witness. Among the issues were the incident at Seneca Rocks, which Farrar — as DiPaolo’s mentor — thought also unfairly tarred him with the same brush, and DiPaolo’s inability to straighten out his life. When the argument ended, Farrar headed off to climb, telling Gregory, “I’ve stood up for Little Dave for 20 years, but now that’s over.”

The death of Geoff Farrar, third from left, was a shocking violation in the climbing community, members say. (Courtesy of Dave Rockwell)

There were no witnesses to what happened next. According to the criminal complaint, DiPaolo told investigators with the Park Police that Farrar had attacked him at Cripple’s Traverse and tried to strangle him. As they wrestled on the ground, DiPaolo said, he found a hammer and hit Farrar to make him stop. That is what Vincent DiPaolo still believes took place. He said his son is not a killer and would have acted only in self-defense. If he fled the scene, it was because he panicked, devastated at what had taken place. “He told me, ‘Dad, I couldn’t breathe. I could not breathe.’ ”

It was right at this time that Gregory finished setting an anchor at the top of a climb called Butterfly and came down to the base of the cliffs. He saw DiPaolo race past him up the trail. Then he turned the corner, past a large protruding nose of rock, and saw Farrar on the ground.

Divers searched the river. The hammer was never recovered, according to the Park Police. But the evidence, as gathered by investigators, doesn’t support self-defense. The head wounds were consistent with being hit from behind, and there were climbers just a few feet away from where Gregory found Farrar and where DiPaolo told investigators the two men fought. The other climbers heard nothing.

When many people discuss DiPaolo’s action, they speak of it in terms approaching treason. Farrar had spent years trying to help DiPaolo, they say, and that help was ultimately rejected.

“He was one of Geoff’s boys,” said Rockwell. “It’s inexplicable that you would betray someone like that.”

But it’s not. Not really. Doug Fields is a Bethesda neuroscientist who studies the inner workings of the brain, and he’s a climber familiar with Carderock and its personalities. A few years ago, he had begun writing a book about rage, what triggers it and the often tragic results. When Fields heard about the killing, he quickly began interviewing participants. Fields said rage is a defense mechanism hard-wired into the brain. It’s a reaction to threats to our personal safety, our self-respect, our territory and other things we hold dear.

“Threat perception triggers unconscious work of the brain,” he said. That’s an explanation, not an excuse. “We’re responsible for our actions.”

He speculates that Farrar’s insults pushed DiPaolo over the edge at a particularly low point in his life. At the time, he was more disheveled than usual, sometimes living out of his van and occasionally catching a nap at the parking lot of the Exxon station by Key Bridge.

Gregory believes it wasn’t the argument itself but the finality of how it ended that was the final straw. Farrar had cut DiPaolo loose, not just from their relationship but by extension the cliffs. “He was exiled from the last place he had,” he said.

Fields’s book, “Why We Snap,” was published in January. He nearly pulled the DiPaolo chapter because the case hadn’t yet been resolved. He said he never thought the judicial process would drag on for more than two years.

DiPaolo spent much of 2014 and 2015 being shuttled between jails and federal detention centers. Because the killing happened at a national park, he was charged with a federal crime. From the beginning, there were significant questions about whether he was competent to stand trial.

The federal public defenders representing him filed a motion to suppress his statements to police, arguing in part that DiPaolo did not “intelligently” consent to waive his Miranda rights. They filed a separate motion signaling their intention to mount an insanity defense. DiPaolo disagreed with the strategy and didn’t always trust his attorneys. During much of this period he was under observation by mental-health professionals. He didn’t believe he was mentally ill, and his attorneys would later argue in court that this showed he wasn’t competent to stand trial because he couldn’t adequately assist in his own defense. It can seem slightly illogical, the need to be mentally competent to help craft an insanity defense, but they represent two states of mind at two points in time. The insanity must be at the time of the alleged crime, while competency is for purposes of assisting in one’s defense.

During DiPaolo’s first competency hearing, on Jan. 23, 2015, he tried to fire his court-appointed attorneys. Referring to Michael CitaraManis, an assistant federal public defender, DiPaolo said: “He keeps bringing up everything that the prosecution can’t bring up, my juvenile records, everything. It just seems like he’s being used as an informant for the government. Can I object at some point?”

At his second competency hearing, on Nov. 5, 2015, DiPaolo had a different plan. He had begun filing motions with U.S. District Judge Deborah Chasanowbefore the hearing, and he was asking to be declared competent to make what many might say is an incredibly incompetent decision: to act as his own attorney. At the end of one motion, he wrote in neat print: “This letter proves I’m competent and can cite law. I won’t cause any problems. I’m no troublemaker.”

DiPaolo also told the judge that he wanted to withdraw his insanity defense. “Defendant had no say in the matter and since it’s wobbley [sic] mostly because defendant doesn’t consent, he wishes to address court.”

There are levels of competency. The U.S. Supreme Court ruled in 2008 that being judged competent to assist in your defense does not mean that you are competent to represent yourself. Chasanow considered the request to waive counsel at a hearing in January. DiPaolo was there, in red jail scrubs, and he sat uneasily next to the public defenders. Chasanow ruled against him, citing among other things the complexity of federal criminal law. That triggered an angry outburst from DiPaolo, which Chasanow saw as further proof that he lacked the restraint to handle his own defense. He needed to work with his attorneys, she said, and to trust them. DiPaolo said he would try.

It’s easy to think that rocks don’t change, but they do, and often at a much faster pace than what we imagine to be geologic time. The lower sections of the cliffs at Carderock are routinely scoured by the floodwaters of the Potomac. The rubbing of all those climbing shoes slowly polishes the small nuggets of quartz that poke from the schist, creating holds that are more slippery and elusive. Occasionally, a handhold will break off, making a route tougher to ascend.

The golden age at Carderock began after World War II and gathered steam in the 1960s, after the opening of the Clara Barton Parkway and the Capital Beltway made the cliffs easily accessible. Until the opening of the Quincy Quarries near Boston in the 1980s, Washington was the only major U.S. city where you could get off work and climb for an hour or two before dark.

Carderock is still popular, particularly on weekends in the spring and fall when the afternoon sun warms the cliffs and summer’s humidity doesn’t yet hang over the river. But the heyday is over. People are busier. Fewer jobs end neatly at 5 p.m. And traffic snarls make it harder to hit the rocks after work.

Carderock is still a popular destination for climbers, but more and more people are taking the sport inside. (Goran Kosanovic/For The Washington Post)

For a growing number of climbers, roping up now means heading to a gym. At an open house at Earth Treks in Rockville, Md., I watched a young woman named Alex work her way with speed and grace up a climb on a concave composite wall studded with brightly colored holds that looked like spare parts from a Mr. Potato Head. She valued the convenience of the gym. It was close to where she lived, and she could just show up with a climbing harness and get going. She’d been to Carderock but never for climbing. She liked hiking on the Billy Goat Trail that runs along the top of the cliffs, past the anchors for Silver Spot, Butterfly and the rest of the routes that zig and zag up the rocks.

DiPaolo entered a guilty plea to the manslaughter charge on Feb. 8, a few weeks after Chasanow’s ruling. He will be sentenced on July 18. According to the plea agreement, the prosecutors and defense have agreed to recommend that Chasanow impose a prison sentence of 10 to 15 years, including time served, followed by a three-year term of supervised release. Vincent DiPaolo said that his son realized the risk of a trial was too great and that there was a possibility of prosecutors upgrading his charge to one with a potentially longer sentence. Both the U.S. Attorney’s Office and DiPaolo’s attorneys declined to comment on any negotiations before the plea agreement.

DiPaolo has put on weight in jail, and he looks pastier than in photos taken before his arrest. His father said his son misses being outdoors, which comes off as a little tin-eared but really is just a reflection of all that was lost in a flash that afternoon, when a different type of rope slipped through Dave’s fingers. DiPaolo could be nearly 50 when he’s free. Vincent DiPaolo said his son won’t return to Carderock. Instead, their plan is to move out West, to another place where there are cliffs close by and where his son can climb again.

Ken Otterbourg is a freelance writer who lives in North Carolina. To comment on this story, e-mail wpmagazine@washpost.com.

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