Shortly after 5 p.m. on Christmas Day, San Francisco Zoo Director Manuel Mollinedo received a call at home: Tigers are on the loose and somebody may have been hurt.
"At first I thought it was a practical or sick joke," he recalled in an interview. "But I took it seriously and grabbed my jacket and got in the car and drove to the zoo."
Soon, the gravity of the situation became all too clear. A Siberian tiger had somehow vaulted from her enclosure, fatally mauling 17-year-old Carlos Sousa Jr. and injuring his two friends.
But other circumstances intensified the horror. The escape took place shortly before dark in a park laced with curving paths and thick stands of foliage. And there was no public address system to alert the few patrons meandering through the zoo.
A placid holiday afternoon had turned frightening and chaotic, with officers uncertain of such basic facts as how many tigers were on the loose. By the time order was restored, the entire zoo had been declared a crime scene and the institution had earned the grim distinction of being the first accredited zoo in the United States in which a visitor was killed by an escaped animal.
"It was almost surreal, the tragedy and emotions that overwhelmed me," Mollinedo said. "It boggled my mind, and my staff was shellshocked."
The incident cast a harsh light on the balancing act that challenges zookeepers everywhere: Keep visitors -- who can be unpredictable and dangerous -- close to, yet at a safe distance from wild animals, who can be equally unpredictable and dangerous.
Zoos and zoo-goers throughout the U.S. are watching the tragedy closely.
"Many of our members are refreshing themselves on safety procedures, reassuring the public that their zoos are safe," said Steven Feldman, a spokesman for the Assn. of Zoos and Aquariums, a zoo accrediting body. "When we learn the full set of facts from this incident, we can make judgments about whether changes should be made in San Francisco or elsewhere."
Much of what happened in San Francisco is still subject to speculation. But investigators are examining the possibility that Sousa and his friends provoked the tiger, a 4-year-old, 350-pound female named Tatiana, which was later fatally shot.
"Police are looking at a 9-inch rock and pine cones and . . . branches or sticks that would not normally be in the tiger's enclosure," said Sam Singer, a zoo public relations consultant. "They're trying to determine how they got there."
Other possible clues have drawn police attention. A shoe print found on a railing next to the wall of the tiger grotto is being checked against the shoes worn by the three friends. A claw mark was discovered atop the grotto wall, indicating that Tatiana leaped over, a source close to the case said. Stains thought to be blood were discovered on a sign and on foliage between the railing and the wall, the source said.
As part of their criminal investigation, police interviewed the two survivors, as well as a San Francisco woman who said she saw four young men taunting the nearby lions that afternoon.
Mark Geragos, a Los Angeles attorney representing the two brothers who survived the attack, has denied that Tatiana was taunted or provoked in any way. He contends the zoo is orchestrating a smear campaign to divert blame in the incident -- a strategy that could be a preemptive defense against the lawsuits the zoo will almost certainly face.
He also suggested that tigers need no reason to attack. "Has everyone forgotten about Siegfried and Roy?" he asked, referring to the mauling of tiger trainer Roy Horn in 2003.
Even if Tatiana was teased, criminal charges are unlikely, legal experts said.
"You'd have to demonstrate that a reasonable person could foresee that taunting a tiger could result in a death," said Rory Little, a professor at UC Hastings School of Law in San Francisco. "A reasonable person, though, would assume the tigers in a zoo couldn't get out. You can go to the zoo any day of the week and see kids taunting animals."
At zoos across the country, the attack has prompted a second look at safety procedures. In Los Angeles, officials are studying the possibility of adding surveillance cameras.