Denver ? Officials on Sunday were trying to determine why a zookeeper killed by a jaguar had opened the door to the animal’s enclosure when zoo policies ban staff members from entering exhibits when big cats are inside.

The Denver Zoo’s feline exhibits were closed Sunday for the investigation. Zoo officials also were interviewing staff members to determine what happened.

The zookeeper, 27-year-old Ashlee Pfaff, had opened a door leading from a service area into Jorge’s enclosure Saturday. A visitor saw the attack from outside the glass enclosure, and his shouts alerted other keepers, zoo spokeswoman Ana Bowie said.