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James Wilson, 40, of Glassboro, New Jersey was killed in the accident.
Investigators want to know whether Wilson was strapped into the bucket of the boom lift as he worked on a church roof. He may have free-fallen to the ground, they said.
"It doesn't appear that he was secured properly. We would expect that he was tethered in," Fire Commissioner Lloyd Ayers said. "We're trying to find out if that's the case."
The vehicle apparently tipped over when it rode over a sidewalk grate, causing the grate to give way, Ayers said.
Crane accidents kill up to 82 construction workers each year in the United States, according to the U.S. Occupational Health and Safety Administration. The figure would likely not include the kind of lift involved in the fatality Monday, according to Celeste Monforton, who studies worker safety as an assistant professor at George Washington University's School of Public Health.
Wilson was pronounced dead at Hahnemann University Hospital shortly after 1:30 p.m.
A co-worker described him as a married father who had worked for their company, Masonry Preservation Group, for more than 20 years.
"He was good people and he was a safe guy," said colleague Robert Howard, who arrived on scene from a nearby project.
The lift struck the corner of a five-story apartment building and knocked down a traffic pole and traffic light before crashing into two parked vehicles on the street.
Three people in cars were treated for minor injuries from falling debris, including a woman in her 70s who suffered a broken arm. Tenants in the 13-unit apartment complex were evacuated, and none were injured. No one was inside the top-floor corner apartment that suffered the most damage.
Tenants have been told they can return at 8 p.m. Monday, according to resident Anna Martin.
"I just heard a really loud crash, and looked out my window and saw the two cars, a car and a truck, smashed in," said tenant Stephanie Watts, 22, who was at home a floor below the damaged unit.
Maintenance work had been under way for about a week on the roof of the First Presbyterian Church near Rittenhouse Square, a park at the center of an upscale neighborhood named for the square. A message left with Masonry Preservation Group of Merchantville, N.J., was not immediately returned Monday.
The lift initially fell relatively slowly but picked up speed after it struck the building, said witness Robert Lee, a construction worker at an unrelated project nearby.
"He didn't scream. He was just trying to work the controls," Lee said.
The Associated Press contributed to this report