Investigators say electrical work was done on a Madison Avenue elevator hours before it crushed a woman to death as she stepped into it on her way up to her office.
The city Buildings Department says the work is now the focus of the investigation.
The company that owned the elevator said it was cooperating with the investigation. In a statement Thursday, it said, "Since Transel was founded in 1989 the safety of our elevators and the security of those who use them has been, and continues to be, our top priority."
In the freak accident Wednesday, the elevator began rising as Suzanne Hart, 41, was boarding the car on the first floor. The doors did not close, and she was pressed between the elevator and shaft wall. Two other people on the elevator were not physically injured but had to be treated for trauma.
Leading New York elevator expert Patrick Carrajat told NBC New York he's seen similar situations -- where an elevator suddenly lurches with someone halfway inside -- only a handful of times.
That it had been serviced just hours before the accident "doesn't bring us to conclusions, but it brings us to suspicions," said Carrajat.
"Of the six accidents that I've had, five of them were attributable to human error," he said.
One publishing executive who works near 285 Madison told NBC New York the horrific accident was all anyone could talk about Thursday.
"People were really worried about what that means for the average New Yorker," said Carol Evans. "We use the elevators every day. Not once, not twice, but many, many times a day."
But Hart's death, said Carrajat, was "probably a million to one shot."
The elevator in Wednesday's accident is one of 13 in the 25-story 1920s tower. It was taken out of use pending the outcome of an investigation, and the building will be closed for the week, the city said.
A buildings department spokesman, Tony Sclafani, said the elevator was inspected in June and no safety issues were found then. The last time the elevator received a violation for a safety hazard was in 2003, and the condition was corrected, Sclafani said.
Hart was a director of business development at Y&R and lived in Brooklyn.
Her grieving boyfriend told NBC New York outside their home: "I loved her. She was a beautiful person."
Hart's former neighbors at her West Village home remembered her as a hard worker who was honest and straightforward.
"It's horrible," said former neighbor Andrea Meyer. "What a terrible thing. Something obviously went wrong."
Hart worked for Y&R, an advertising firm in the building.
Y&R said it was "deeply, deeply saddened."
"Our focus at this moment is the well-being of the employee's family, and our larger Young and Rubicam family," said CEO Peter Stringham. "As you can imagine, this is a great emotional shock to all of us."