The San Francisco Zoo director said Thursday that the wall surrounding the enclosure housing the tiger responsible for a teenager's Christmas day death was much lower than is recommended by the country's primary zoo accrediting agency.

Two days after the cat escaped and attacked three young men, Zoo Director Manuel A. Mollinedo acknowledged that the wall was 12 1/2 feet — well below the 16.4-foot minimum height suggested by the Association of Zoos & Aquariums.

Mollinedo said safety inspectors had examined the wall and never raised red flags about its size.

"When the AZA came out and inspected our zoo three years ago, they never noted that as a deficiency," Mollinedo said. "Obviously now that something's happened, we're going to be revisiting the actual height."

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On Wednesday, Mollinedo said that the wall was 18 feet high, and that the moat around the tiger's pen was 20 feet wide.

Investigators have yet to say how the tiger got out of the pen. But based on Mollinedo's initial estimate of the height of the wall, animal experts expressed disbelief that a tiger in captivity could make such a spectacular leap.

Earlier Thursday, the father of the 17-year-old victim of the tiger attack broke down as he described the loving relationship he had with his son — and he said he wanted answers about how the animal got loose.

"He's my only son. He's all I got," a weeping Carlos Sousa told reporters. "This is very difficult for me."

Carlos Sousa Jr., 17, was one of three young men attacked by a Siberian tiger at the San Francisco Zoo near closing time on Dec. 25; he died on the scene. The other two were brothers who were severely mauled.

Police were investigating whether one or more of the three may have taunted the animal before its deadly attack.

"I need evidence; I need proof," Sousa said during the press conference outside his house. "My son wasn’t alone when this happened. ... I really would love to talk to them and get some information about what happened."

The two injured men, 19- and 23-year-old brothers from San Jose, remained in stable condition at San Francisco General Hospital. They suffered deep bites and claw wounds on their heads, necks, arms and hands, said Dr. Rochelle Dicker, a surgeon. She said they were expected to recover fully.

Dr. William Schecter of San Francisco General, who is overseeing the survivors' care, told a news conference Thursday that he had visited both young men that morning and they were doing well.

"They're being held because of their wounds. They're not going to be released today," Schecter said.

He said he expected that the brothers would be able to go home in "the next several days."

"From a physical point of view, they're going to return to full function," Schecter said, declining to comment on their mental prognosis or on other details of their injuries.

Sousa told ABC's "Good Morning America" that he didn't think his son would have provoked the tiger.

"I don't think my son would do something like taunt animals," he said Thursday morning. "It's unbelievable, but only the evidence can prove that. And right now I can't say much."

Police shot the 300-pound animal to death after it killed Carlos Sousa Jr. and seriously wounded the other two victims.

Investigators found a shoe and blood in an area between the gate and the edge of the animal's moat, raising questions about whether one of the victims dangled a leg or other body part over the edge of the water, according to The San Francisco Chronicle.

Police on Thursday could not confirm the Chronicle's report to The Associated Press.

Police Chief Heather Fong said Wednesday the department opened a criminal investigation to "determine if there was human involvement in the tiger getting out or if the tiger was able to get out on its own."

The zoo remained closed Thursday.

One zoo official insisted the tiger did not get out through an open door and must have climbed or leaped out. But Jack Hanna, former director of the Columbus Zoo, said such a leap would be an unbelievable feat and "virtually impossible."

Instead, he speculated that visitors might have taunted the animal and perhaps even helped it get out by putting a board in the moat.

Ron Magill, a spokesman at the Miami Metro Zoo, also said that it was unlikely a zoo tiger could make such a leap, even with a running start.

"Captive tigers aren't nearly in the kind of shape that wild tigers have to be in to survive," he said.

Provoking the animal definitely can make it more aggressive, but "whether it makes it more likely to get out of an exhibit is purely speculative."

The same tiger, a 4-year-old female named Tatiana, 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.

Zoo director Manuel Mollinedo said Wednesday 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."

It was unclear how long the tiger had been loose before it was killed on the 125-acre zoo grounds. Four officers hunted down and shot the animal after police received an emergency call from a zoo employee.

The zoo has a response team that can shoot animals. But zoo officials and police described the initial moments after the escape as chaotic.

The first attack on Carlos Sousa Jr. happened right outside the tiger's enclosure. Another was about 300 yards away, in front of the zoo cafe. The police chief said the animal was mauling one of the survivors, and when officers yelled at it to stop, it turned toward them and they opened fire.

Only then did they see the third victim, police said.

The victim's parents told the AP they did not know why their son went to the zoo Tuesday.

Carlos Sousa said his son loved playing, recording and writing music, and he made friends wherever he went.

"He's a fun person — he gets along with everybody," said Sousa, choking back tears. "He doesn't have enemies. Every time I see him, we hug and kiss. He always says he loves me; I always say I love him."

He and the teen's mother, Marilza Sousa, said they learned of their son's death from the coroner, who called to tell them the news. Neither the police nor zoo officials contacted them, according to the Sousas.

Said Marilza Sousa: "I wish I was sleeping and this was just a bad dream, but it's not."

FOX News' Catherine Donaldson-Evans and The Associated Press contributed to this report.