Suzanne Hart, a 41-year-old executive at one of Manhattan’s most prominent advertising firms, was stepping into the elevator of an 85-year-old Midtown office building around 10 a.m. Wednesday, just as she had every workday for the past four years, while fellow workers streamed into the mosaic-tiled lobby.

Then, in an inexplicable instant, after Ms. Hart placed one foot inside, the elevator suddenly lurched up, its door still open, according to the Fire Department. It dragged her until she was pinned between the elevator and the wall, between the first and second floors, the police said.

Two passengers in the elevator car could only watch in horror, and would remain trapped in the elevator for an hour before rescuers could free them.