Investigators were searching for suspects in the city's bloodiest crime in a decade after four men were fatally shot in a basement that neighbors said had been set up as a music studio.

Three men were found dead at the house and the fourth died at a hospital, Police Superintendent Bobbie Johnson said. They were in their late teens and early 20s, authorities said.

Johnson said witnesses told police they saw a heavyset person fleeing the scene Tuesday night. No arrest had been made.

Tia Duncan, who said she moved out of the house on Monday, said her brother was one of the victims. Edwin Duncan, 21, was part of a rap group and lived in the house where the shootings occurred, she said.

He and a bandmate were waiting in the basement for other members of the group to arrive when the shootings took place, Tia Duncan said.

Police did not confirm that Edwin Duncan was one of the victims, but said those involved appeared to have known each other. Police Commissioner Kathleen O'Toole said one of the victims lived in the house.

"It's much too early to speculate on a motive in this incident," O'Toole said. "But generally speaking, homicides occurring inside residences are seldom random acts of violence."

Tuesday's killings were among the worst in Boston's recent history.

In 1995, four people were gunned down at a crowded restaurant in the city's Charlestown neighborhood. In 1991, five men were shot execution-style in a social club in the city's Chinatown neighborhood.

The deaths pushed the number of murders in Boston this year to 71, the highest in a decade, and frustrated efforts by city officials to stem the wave of violence.

U.S. Attorney Michael J. Sullivan said last week that his office will increase federal prosecutions of suspects involved in gun and gang violence in Boston.

The house on Bourneside Street is a triple-decker typical of the multifamily homes that dot Boston's working-class neighborhoods. It's near Fields Corner, a mostly gentrified neighborhood of stately Victorians.

The Rev. Jeffrey Brown, a co-founder of an anti-violence coalition who lives nearby, said police had not had any problems at the address in the past.

Brown said he and other ministers have been trying to take steps to lower the level of violence in the city.

"We have to rise up now and fight this culture of intimidation and indifference that breeds this kind of violence," he said.