The unidentified victim apparently fell accidentally after summoning the elevator at 55 New Montgomery St. over the weekend, investigators said. It was unclear how far he fell.

The body was found after there was trouble reported with the elevator, authorities said. Investigators said surveillance videotape shows the victim waiting for the elevator, but it was not immediately known what floor the video was taken on.

Investigators with the state Occupational Safety and Health Administration are looking into how the accident happened, police said. Officials said they would investigate any possible malfunction of the elevator.

The building is considered historic, and “the elevator itself is part of a historic site,” said Erika Monterroza, a CalOSHA spokeswoman.

E-mail Jaxon Van Derbeken at jvanderbeken@sfchronicle.com.