A Bolivian-born jaguar that killed a Denver zookeeper was well-behaved as a young cat but his twin was so mean that his handlers named him Osama, a Bolivian zoo official said Monday.

Ashlee Pfaff, 27, died from a broken neck and other injuries after the big cat named Jorge attacked her while she was inside an employee hallway that opened into his outdoor enclosure on Saturday, the coroner said. A zoo employee shot and killed Jorge when he approached emergency workers trying to save Pfaff.

Jorge — Spanish for George — had been named after President Bush, said Margot Ugarteche, a veterinarian at the Santa Cruz Municipal Zoo of South American Fauna in Bolivia, which sent Jorge to the Denver Zoo.

"Osama was always the more dominant of the two," Ugarteche said. "He was always rough with Jorge. That was the relationship we saw between them.

"Jorge wasn't bad, really," she said. "I don't know what could have happened. Perhaps because he was so well-behaved, the trainer (in Denver) thought she could trust him. But you never know with wild animals."

Denver Zoo officials said zoo policy prohibits keepers and big cats from being in an enclosure together. Jorge should have been locked in before the door to the outdoor exhibit was open.

Pfaff was working alone and the investigation found no faulty doors, locks or gates, zoo spokeswoman Ana Bowie said.

"We don't know if she was going in, and we never will," Bowie said. "Why that door was open and what she was doing, we do not know."

Pfaff had undergone regular safety training for the jaguar exhibit, shadowed veteran keepers and attended mandatory safety meetings, officials said. A New Mexico native, she graduated with a biology degree from New Mexico State University in 2002 and started work at the zoo in 2005.

"Ashlee was a great zookeeper, she was dedicated to this institution, dedicated to her animals," Bowie said.

Lynn Kramer, a veterinarian who heads the zoo's biological programs, said zoo employees' practice of working alone could change as officials review the incident.

Kramer said employees have drills at least four times a year for the escape of an animal capable of killing a human. He said four of the 16 employees trained in firearms responded within minutes of the attack on Pfaff.

At the entrance to the zoo, friends and zoo visitors piled flowers and notes in Pfaff's honor.

Pfaff's family said they want to know what happened and are confident the investigation by the zoo and Denver police will answer their questions. The family is "mourning her sudden and tragic death. Ashlee was a beautiful person, and was loved by many," the statement said.

The U.S. Agriculture Department, which inspects zoos at least annually, also planned to investigate, spokesman Darby Holladay said.