Warning sign posted near door that crushed San Francisco Zoo's gorilla

SAN FRANCISCO (KABC) -- New details are emerging about an accident that killed a young gorilla at the San Francisco Zoo.

ABC News affiliate KGO-TV has obtained an image of a sign posted next to the hydraulic door that crushed the 16-month-old animal that says employees operating the door are supposed to keep a hand on the stop button at all times.

It reads: "To prevent injuries to the gorillas during operation of the electric doors: Move only one door at a time. Keep your hand on the stop button at all times. Do not leave the electric panel until operation of the door is complete."

Similar to those on garage doors, the emergency stop button controls the door. And now, investigators are looking into whether the zoo employee failed to follow procedure.

The baby gorilla, named Kabibe, died on Friday when zoo keepers were moving the primates into their night quarters.

In a statement, the zoo employee said the incident happened after Kabibe was carried into the night enclosure by her grandmother and primary caregiver Bawang.

The zoo employee's name and work history have not been released. It's not yet known if she is facing disciplinary action.

Animal rights advocates say the stop button could have saved the baby gorilla.

Kabibe had been one of the zoo's stars, and was a rare example of a birth in captivity.

The San Francisco Zoo has hired a renowned gorilla expert to investigate the accidental death.

The Associated Press contributed to this report.