(AP) -- A huge construction crane being lowered to safety in a snow squall plummeted onto a Lower Manhattan street Friday, killing a Wall Street worker and leaving three people hurt by debris that scattered as the rig's lengthy boom fell, officials said.

The mobile crane's boom landed across an intersection, smashed several car roofs and stretched much of a block after the accident around 8:25 a.m. at a historic building about 10 blocks north of the World Trade Center.

Robert Harold heard a crashing sound as the rig fell right outside his office window at the Legal Aid Society.

"You could feel the vibration in the building," said Harold, who recounted seeing onlookers trying to rescue someone trapped in a parked car and seeing a person lying motionless on the street. After the collapse, the crane's big cab lay upside-down in the snow with its tank-like tracks pointed at the sky.

The collapse killed David Wichs, a mathematical whiz who worked at a computerized trading firm, his family said. Born in Prague, he had immigrated to the United States as a teenager and graduated from Harvard University, said his sister-in-law, Lisa Guttman.

"He really created a life for himself. He literally took every opportunity he could find," she said through tears.

Mayor Bill de Blasio initially said the person killed in the collapse was in a car, but police later said he was on the sidewalk. De Blasio said two people were seriously injured, while a third suffered more minor injuries.

A bystander video taken through a window high above the ground showed the arm descending, then taking the entire crane to the ground.

The accident happened as workers were trying to secure the crane against winds around 20 mph by lowering the boom, which had been extended to as long as 565 feet the day before, officials said. Because the crane was being lowered, workers were directing pedestrians away from it on a street that otherwise would likely have been teeming with people.

"Thank God we didn't have more injuries and lose more people," de Blasio said. "It's something of a miracle that there was not more of an impact."

Officials were working to determine why the crane fell. An employee who answered the phone at the offices of crane owner Bay Crane would say only that an investigation was underway and wouldn't give his name. The company officials identified as the crane operator, Galasso Trucking Inc., didn't immediately respond to messages about the collapse.

Capable of lifting 330 tons, the rig had been working for about a week to replace air conditioning equipment and generators on the roof of 60 Hudson Street, a 425-foot-tall, Jazz Age skyscraper that once housed Western Union, officials said. City building inspectors had been at the site only Thursday because the boom was being extended so it could reach farther onto the roof, de Blasio said.

Buildings Commissioner Rick Chandler said inspectors found no problems then with the crane but would investigate further.

The building's owners declined to comment.

Nearby buildings were evacuated after the collapse while fire and utility officials checked and rechecked for gas leaks.

Crane safety came under scrutiny in the city after two tower cranes collapsed in Manhattan within two months of each other in 2008, killing a total of nine people. The accidents spurred fueled new safety measures, but there have been a number of crane accidents in the city over the years since.

___

This story has been corrected to show that the collapse happened Friday, not Thursday.

___

Associated Press writers Kiley Armstrong, Jake Pearson, Jennifer Peltz and Ula Ilnytzky contributed to this report.