A zoo spokesman called the claim "unreliable."
Attorney Mark Geragos told The Associated Press that Paul Dhaliwal, 19, and Kulbir Dhaliwal, 23, tried to get help for their friend, Carlos Sousa Jr., after unsuccessful attempts to stop a 350-pound Siberian tiger that had attacked Sousa.
According to Geragos, the tiger initially attacked Sousa and Paul Dhaliwal at about 4:30 p.m. While Sousa was seriously hurt, Paul Dhaliwal escaped, and he and his brother ran 300 yards to a zoo cafe where they had eaten earlier.
But Geragos said the brothers were "denied entry" to the cafe because the zoo was closing. At that point the brothers lost sight of the tiger.
The brothers then spotted a female security guard who appeared "diffident" when told of the escaped tiger, Geragos said.
"Who knows what would have happened if the guard had acted earlier?" Geragos said. "But Carlos would have stood a better chance of not dying. And maybe the police would not have shot the tiger as well."
Geragos said the tiger returned and began mauling Kulbir Dhaliwal before police officers arrived and shot and killed the animal.
Zoo spokesman Sam Singer dismissed Geragos' claims as unreliable and noted that the San Francisco police have not even finished their investigation.
"I never speculate on defense attorney hypotheses," Singer said late Tuesday in a phone interview.
According to police dispatch logs from the day of the attack, someone inside the cafe called 911 at 5:07 p.m. It is unclear when the brothers tried to notify people in the cafe about the attack.
The dispatch logs also show that zoo employees initially questioned whether early reports of the attack were coming from a mentally unstable person.
By 5:10 p.m. zoo employees reported that a tiger was loose, and by 5:13 p.m., the zoo was being evacuated and locked down.
For several minutes, the medics refused to enter the zoo until it had been secured. Meanwhile, zoo keepers believed several tigers were loose, and hoped to tranquilize them.
"Zoo personnel have the tiger in sight and are dealing with it," reads a 5:17 p.m. note on the transcript.
By 5:20 p.m., medics had located one victim with a large puncture hole to his neck. The tiger was still loose.
As medics attended to the victim, an officer spotted the tiger sitting down before it fled and began attacking another victim, according to the logs.
At 5:27 p.m., less than 20 minutes after the initial reports, the officers began firing and killed the tiger.
Zoo officials say the tiger likely climbed over the wall of its enclosure, which was about 4 feet below the recommended minimum for U.S. zoos.
Meanwhile, the tiger exhibit at San Francisco Zoo will not close down despite the Christmas Day escape, a zoo spokesman said Monday, reports CBS News affiliate KPIX-TV.
The city's Recreation and Park Department is planning new security enhancements to the zoo's tiger grotto that will be in place in 30 days, said spokesman Sam Singer.
The new security will be designed by the same architects who completed the zoo's grizzly bear habitat in June and who were also commissioned to work on renovating its hippopotamus exhibit.
"There are no plans on closing the (tiger) exhibit down whatsoever," Singer said. "They're designing the (security enhancements) as we speak," reports KPIX-TV.