Family and friends are struggling to comprehend the death of Paul Gilligan III, a recent Harvard graduate who fell six stories from a college roommate’s Upper West Side apartment early Friday morning.

The 22-year-old New Jersey native, who received his degree June 9, went out Thursday night with two of his best friends to watch Game 7 of the National Basketball Association finals, according to his sister, Lindsey Gilligan, 20. After drinking a few beers, Gilligan, Daniel Seltzer, and Stephen Robbins walked to Mr. Seltzer’s apartment on Central Park West between 93rd and 94th streets. They entered just after 2 a.m., Ms. Gilligan said, and Mr. Seltzer blew up an air mattress for Gilligan and went to sleep in his bedroom.

“After that, no one really knows what happened,” Ms. Gilligan told The New York Sun.

Mr. Seltzer woke up at about 7 a.m., saw the air mattress was empty and the window open, and assumed his friend had gone for a run. Before long, Ms. Gilligan said, police knocked on the door and asked Mr. Seltzer to identify a picture of Gilligan’s body, which a building worker had discovered in an adjacent alley at 6:30 a.m.

Ms. Gilligan said she and her family assume that Gilligan woke up in the middle of the night to get some fresh air and fell out because “the window bar cut off below his knees.”

“Paul was a real heavy sleeper, he would sometimes get up and be groggy and disoriented,” she said. “I wish I knew more because it would make it so much easier to understand things. But there is no comprehensible way that this was a suicide.”

An autopsy established that Gilligan died of injuries sustained in the fall, but the circumstances leading to his death are still under investigation, a spokeswoman for the city Medical Examiner’s office, Ellen Borakove, said.

The mystery surrounding Gilligan’s death troubles his father, Paul Gilligan Jr.

“When I talked to him at 6 p.m. that night, he was giddy and on top of the world, telling me about all the things he did in New York,” Mr. Gilligan said.

Those close to him remember Gilligan as a high-achieving and dedicated student who excelled in many sports, from soccer and basketball to baseball and crew. A native of Haddon Township, N.J., he majored in biology and graduated magna cum laude. He was planning to travel to Europe on a fellowship to teach soccer before applying to the nation’s top medical schools for 2006 admission.

At Harvard, Gilligan was randomly matched up with eight roommates at the start of his freshman year, and the group clicked instantly. They chose to live together all four years.

One roommate, Bryan Smith, said he made the junior-varsity soccer team freshman year but Gilligan did not.

“That entire summer he worked on his soccer game,” Mr. Smith said. “The next year, I didn’t make it and he did. He even moved up to the varsity team. He was one of the most driven people I’ve ever met.”

Another roommate, Ryan Lynch, said one of the first stories Gilligan ever told him revealed his almost superhuman determination.

“He said he had glasses at one time but he willed his eyesight better,” Mr. Lynch said. “It summed up his attitude: There was never anything he couldn’t overcome.”

Mr. Smith said Gilligan operated on a schedule that he dubbed the “Six Hour Plan.”

“He’d go to bed at midnight and wake up at 6 a.m., work out, eat breakfast, and go study,” Mr. Smith said. “Some mornings I would wake up at 7 a.m. and I would hope Paul was still asleep, but he was always up.”

Another college friend who dated Gilligan for two years, Laura Spence, said she met him when they were lab partners in biology class and she discovered they were “thoroughly incompetent at all the drawings of cells, plants, and animals we were forced to do.”

Last year, Ms. Spence and Gilligan took a hiking trip to Europe, where she said they “hiked a rocky, windswept trail to the border of Austria and Italy, saw no other people the entire route, and then had a picnic at the top of a ridge perched above two valleys.” Ms. Spence attends medical school in her native England but flew to New Jersey for Gilligan’s funeral and wake.

A professor of romance languages and literature at Harvard, Lino Pertile, who oversees Gilligan’s dormitory, wrote in an e-mail that “it is almost impossible to comprehend that he is no longer with us.

“He never sought to be the center of attention, but he took genuine pleasure in contributing to the life of others around him,” Mr. Pertile wrote.

Mr. Smith said Gilligan sent an email to the dorm congratulating those who had performed well in an intramural running race, failing to mention that he had placed first.

“He was just so incredibly humble about his talents,” Mr. Smith said. “I don’t think we knew how lucky and fortunate we were at the time. I know we’re all going to take away something from him that dictates how we lead the rest of our lives.”

Haddon Township High School’s varsity soccer coach, Michael Green, met Gilligan when he was a seventh-grader and said athleticism did not come easily to him then.

“If you knew him in the years when he wasn’t the strongest or had the best conditioning or the best endurance, and you were with him when he put in all the hours, you think this was a kid who had an incredible ability to focus,” Mr. Green said. “It never surprised me when he made Harvard’s varsity that spring. He wanted to prove he could play at that level.”

Mr. Green said Haddon Township, a close-knit community of 14,000 residents in southern New Jersey, was “devastated” by Gilligan’s death.

“If you needed help with a camp or a clinic, you called Paul, and Paul was there,” Mr. Green said. “I don’t know how this community is going to handle it, because it’s lost its best and brightest. He kind of represents the community in a lot of ways. It was just assumed you would track Paul’s life because Paul was going to do something special.”