As police investigate the escape of a 300-pound Siberian tiger from its high-walled enclosure at the San Francisco Zoo, wildlife experts are disagreeing about whether it could have possibly leapt the 18-foot wall and 20-foot moat on its own.

Video: Tiger Runs Wild

The zoo's director of animal care insists the tiger, Tatiana, did not leave through an open door. He said that she must have either climbed or leaped out.

The tiger killed Carlos Sousa Jr., 17, of San Jose, Calif., and wounded two other men on Tuesday. It was shot and killed by police.

Naturalist Sy Montgomery, who has written about tigers, said a tiger could have made the jump if it was amazingly athletic.

But Jack Hanna, former director of the Columbus Zoo, said the theory "doesn't add up." He said such a leap would be an unbelievable feat and "virtually impossible." And Ron Magill of the Miami Metro Zoo said even with a running start, it is unlikely a zoo tiger would be in the physical condition that might enable a wild tiger to make such a jump.

Hanna speculated that visitors might have taunted Tatiana and perhaps even helped her by doing something like putting a board in the moat.

Police Call Zoo Crime Scene

The zoo remained a crime scene Wednesday as authorities tried to piece together Tuesday's incident.

Police Chief Heather Fong said they were not certain whether the incident involved any "human action."

Police did say they're confident there were no other victims. They searched the zoo grounds during the night using searchlights and thermal imaging equipment, and again during daylight.

The same tiger ripped the flesh off a zookeeper's arm just before Christmas a year ago while the woman was feeding the animal through the bars. A state investigation faulted the zoo, which installed better equipment at the Lion House, where the big cats are kept. The San Francisco Chronicle said the zoo was slapped with an $18,000 penalty.

Zoo director Manuel Mollinedo said Wednesday that he gave no thought to destroying Tatiana after the 2006 incident, because "the tiger was acting as a normal tiger does." As for whether Tatiana showed any warning signs before Tuesday's attack, Mollinedo said: "She seemed to be very well-adjusted into that exhibit."

Two Victims Stable

The two injured men "are in very stable condition and are in good spirits," said Rochelle Vicker of San Francisco General Hospital. "They look absolutely fantastic."

Vicker said the key to their recovery will be to make sure they don't develop infections as a result of their wounds. The victims were listed in critical but stable condition, with deep bites and claw cuts. An emergency room doctor told ABC's "Good Morning America" the injuries are severe but "very treatable."

The San Francisco medical examiner had not been able to identify the dead man, officials said. The man did not have any identification and no one had called asking about him.

A fire department spokesman called it a tragic event for San Francisco. He said the city prides itself in the zoo and in tourists coming to see the city.

911 Call Alerts Police

Police were alerted to the escape by a 911 call from a zoo employee just after 5 p.m. on Tuesday.

Officers said they found the body of the first victim outside the tiger's enclosure when they entered the dark zoo grounds.

The second victim was about 300 yards away, in front of a cafe. The man was sitting on the ground, blood running from gashes in his head and the tiger was sitting next to him, police said.

The tiger attacked the man again and officers approached the tiger with their handguns, police said. When the tiger moved in their direction, several of the officers fired, killing the animal.

Only then did they see the third victim, who had also been mauled.

About 20 visitors were in the zoo when the attacks happened about an hour before the 6 p.m. closing time, officials said. Employees and visitors were told to take shelter when zoo officials learned of the attacks, and some employees locked themselves inside buildings as they had been instructed to do if an animal escaped.

There were five tigers at the zoo - three Sumatrans and two Siberians. Officials initially worried that four of them had gotten loose.

The zoo was closed on Wednesday and will remain closed at least through Thursday, officials said.