A tiger escaped its enclosure at the San Francisco Zoo, killing one visitor and mauling two others on Christmas. Zoo officials were still uncertain how long the Siberian tiger, the same one that mauled a zoo keeper almost one year earlier, had been loose before being killed by police. The attack occurred just after the 5 p.m. closing time, on the east end of the 125-acre grounds. The zoo's director of animal care and conservation, Robert Jenkins, could not explain how Tatiana escaped. The tiger's enclosure is surrounded by a 15-foot-wide moat and 20-foot-high walls, and the approximately 300-pound female did not leave through an open door, he said. "There was no way out through the door," Jenkins said. "The animal appears to have climbed or otherwise leaped out of the enclosure."