The Friday night party started off low-key, with about 20 college students and other young adults chatting and sipping beer inside a fourth-floor apartment in Boston's Allston neighborhood.
Shawn Dow, a student at Art Institute of Boston, was in the small crowd, engaged in carefree conversation with fellow partygoers.
Then, about 1:30 a.m. yesterday, three uninvited men showed up at the door, witnesses said. One party crasher got into a heated argument with a woman inside the apartment, touching off a brawl in the building's stairwell that involved about 20 males, witnesses said.
Dow, law enforcement officials said, was not involved.
But an hour later, the 21-year-old photography major was dead.
Authorities say Dow apparently, and accidentally, fell off the building's black-top roof, landing in an alley behind the sprawling four-story red-brick complex that stretches almost the length of Glenville Avenue.
Homicide detectives interviewed dozens of witnesses. "Preliminary information suggests the victim was not part of that scuffle, that he was injured as a result of falling from the roof," said Elaine Driscoll, a Boston police spokeswoman.
"There will be an autopsy [early this week], and that may yield more clarity as it relates to the nature of his injuries. We do not believe that he was beaten up. The police found him in the alley as a result of being called to the house because of the altercation, but the two incidents appear to be separate," she said.
Some of Dow's friends and classmates who attended the party disputed the police account, saying a beating in the brawl left him unconscious and bleeding. They said no one went to the roof.
Dennis Magarian said he showed up at the party at 12:30 a.m. about an hour before the unwanted guests. One argued with a woman at the party after she asked the three to leave. Two of the uninvited guests pulled the man who had been arguing with the woman out of the apartment.
"We shut the door when they left," Magarian said. Then, as the three men walked down the stairwell, they got into an altercation with second-floor residents. "We heard a lot of screaming and noises coming from below, and some of the guys inside our party rushed downstairs."
Magarian said friends of the three uninvited guests also rushed into the building and the fight escalated. Beer bottles were thrown, wooden spindles broken from the handrails were used as weapons, and there was kicking and punching, Magarian said.
Dow's mother, Dorothy Glenn, said her son was a junior at the institute and wanted to work as a photographer after he finished school.
"He wanted to work for a magazine," his mother said in a telephone interview last night. "He told me he had to live in Boston because it was the only place he could get a job to start out. He was a regular kid, a good kid. He was my son. I loved him. It's still new. I don't even really believe it yet."
Glenn said her son has an older brother, David, and graduated in 2005 from Peabody High School. Shawn recently moved from Jamaica Plain to an apartment in Allston to reduce the commute to his classes. She said he would never hesitate to help out his friends.
"He had a friend serving in Iraq, and Shawn helped his mom and dad move while he was [in Iraq]. He stayed the extra hours helping them after the other friends had left. He was a good kid."
Friends described him as a popular guy who loved to spend time with them.
"It's hard to even think of what happened to him," said Bradley DiFoggio of Allston, who left the party before the fight and said he was Dow's best friend and former roommate. "I was sitting with Shawn [at the party], and he was fine. We were just laughing, talking about our weekend plans, and that was it. That was the last time I spoke with him." DiFoggio, a design major at the institute, said Dow worked part time at Marty's Liquors in Allston, manning the deli.
Joe Hession, the store manager at Marty's, said Dow worked for him for about eight months and was one of his hardest workers. "He was one of the best employees we had," said Hession. "We're all just saddened by this. It's just a travesty."
Lucia Tenuta, 19, a sophomore at Lesley University who met Dow through a mutual friend, said she showed up at the party about 11 p.m. and ran into Dow as she left about 12:30 a.m. When she left, Dow spilled what she was drinking and apologized, Tenuta said. The last words he said to her were "I love you," she added.
Tenuta said Dow, and most of the people at the party, had been drinking beer.
Dow's brother, David, a senior at the Massachusetts College of Art, said his sibling enjoyed partying, but was "never one to overdo it."
David said his brother got into photography during high school. "He found art as a way to express himself, a way of acceptance. He liked documenting . . . his view of the world."
Jane Tuckerman, a professor of photography at the institute who was reached by phone yesterday at her house in Dartmouth, said Dow "was quiet, but he was very nice, a good kid. . . . It's just so tragic."
Globe correspondent Jeff Elliott contributed to this report.