Tatiana , a 4-year-old Siberian tiger fatally attacked one zoo visitor and injured two others at the San Francisco Zoo last Christmas afternoon. She had to be killed by police officers . "She was everything that a tiger is supposed to be," says big-cat expert Ronald Tilson. "She was essentially shot and killed for being a tiger."

Yet , this was not a one-off incident. An year ago, Tatiana mauled her keeper, devouring the flesh from her arm. Should Tatiana have been put down at that time , is what is haunting zoo officials now.

"There was no reason whatsoever," says Tilson, director of conservation at the Minnesota Zoo. Since 1987 , he has been overseeing the tiger species survival plan of the Association of Zoos and Aquariums.

Louis Dorfman, an animal behaviorist with the International Exotic Feline Sanctuary in Boyd, Texas, supports the idea that Tatiana posed no greater danger than she had before Dec. 22, 2006 . Then, she had reached under the bars of her cage and seized the arms of zoo employee Lori Komejan as dozens of people watched.

"We have 60 cats here," Dorfman says . "Any one of them would have done the same thing. But they would forget about it 15 minutes later. They don't dwell on things. The only thing they dwell on is if someone mistreated them."