Geragos said his investigators have interviewed a former zoo employee who said that sometime in the last five years, a tiger perched atop the wall and had to be coaxed back into the enclosure. He declined to identify the ex-employee.
A zoo spokesman said that "no one at the zoo is familiar with any close calls involving a big cat in the last five years or any instance of a tiger or lion on the edge of the grotto."
Whether the recommended 16-foot barriers could have prevented Tatiana's escape is an open question.
Some animal experts say she must have been worked into an adrenaline-fueled rage to bolt in the first place.
"She had to be in a hyperaggressive state," said Chris Austria, a former animal trainer who worked with tigers at the former Marine World in Vallejo, Calif., and with bears at the San Francisco Zoo. Without some extraordinary stimulus, "it is really unlikely that a 350-pound tiger would jump up 12 1/2 feet and hold on with her paws and pull herself up," he said.
Animal trainer Diana L. Guerrero said that zoo tigers become desensitized to yelling or verbal taunting but that someone throwing or dangling things into the enclosure could be enough to trigger an escape.
"In the history of zoos, unless an animal is highly motivated to escape, they usually don't," said Guerrero, who has been affiliated with zoos in San Francisco, Los Angeles and elsewhere.
But it wasn't the first accident to occur at a U.S. zoo.
Last February, a jaguar at the Denver Zoo fatally mauled one of his keepers. In 2004, an escaped gorilla at the Dallas Zoo lifted up a toddler with his teeth and attacked three people before being shot to death 40 minutes later.
Still, the zoo association, which includes 182 institutions in the U.S. and Canada, describes zoo-going as a very safe experience. Last year, 157 million people visited the organization's zoos and aquariums. The tiger attack was the first fatal attack of a zoo patron since the group started accrediting zoos in 1974, officials said.
In San Francisco, Tatiana mauled a zookeeper at feeding time in December 2006. The woman survived and has filed a lawsuit against the zoo.
Before Sousa's death, the San Francisco Zoo's biggest recent controversy centered on its elephants. After two of them died within weeks of each other in 2004, and under pressure from county supervisors, the zoo placed its remaining elephants in a sanctuary.
