The zoo's big-cat enclosure will remain closed indefinitely, but many visitors on Thursday said they wanted to show their support for the facility.
"They do their best to keep everybody safe," said Dianne Todd, of Sunnyvale, who was there with her two young sons.
Zoo spokesman Paul Garcia said the zoo is installing a public-alert system that would broadcast an alarm to notify zoo staff of any emergency. Employees could then use portable speakers to give instructions to visitors.
The improvements were made as police investigated whether the tiger's victims had taunted the animal before it climbed or leaped out of its outdoor pen. Carlos Sousa Jr., 17, was killed, and his two friends were severely injured.
"All I know is that something happened to provoke that tiger to leap out of her exhibit," zoo director Manuel Mollinedo said Wednesday. He declined to elaborate because the police investigation was not yet complete.
On Thursday, zoo officials invited visitors to bring items in remembrance of Sousa and the tiger, which was shot dead by police during the attack.
Some visitors placed flowers, cards and photographs of the animal beside a sculpture of a bronze tiger that has stood near the zoo entrance since before the mauling. An animal-rights group planned a candlelight vigil for Sousa and the tiger.
A woman has claimed she saw three men teasing the animals shortly before the tiger attack, according to a report on the Web site of the San Francisco Chronicle. Jennifer Miller, who was at the zoo on Christmas with her husband and two children, said the family left the area because her kids were disturbed by the young men's behavior.
"The boys, especially the older one, were roaring at them. He was taunting them," Miller told the newspaper.
Police talked to Miller on Wednesday, but were not able to corroborate reports that the victims taunted the tigers. They also could not substantiate Miller's claim that a fourth person was with the attack victims, or what effect the taunting she described might have had.
"I don't know if what they did was any more than what kindergartners do at the zoo every day," Inspector Valerie Matthews told the Chronicle.
Miller said Sousa, whom she later recognized in newspaper photos, was not harassing the animals.
Police spokesman Sgt. Steve Mannina said investigators were looking into whether alcohol was a factor in the attack. Toxicology tests on Sousa's body have not been completed, and results will probably not come back for several weeks, according to the San Francisco medical examiner's office.
Mark Geragos, an attorney for the survivors - brothers Kulbir Dhaliwal, 23, and Paul Dhaliwal, 19 - said none of the victims did anything to goad the tiger into breaking loose.
"That's just nonsense," Geragos said. "There is no evidence of taunting whatsoever because there was no taunting."
Earlier this week, he said the zoo was slow in its response to the escaped tiger, an assertion at least partially backed up by police dispatch logs showing that employees initially questioned whether early reports of the attack were coming from a mentally unstable person.
Mollinedo brushed off Geragos' claims Wednesday, saying he was satisfied with the employees' response. He declined to elaborate, citing the investigation.
Zoo officials say the tiger likely climbed out of an empty moat that separated the public from the animal's enclosure, which had a 12½-foot wall, making it 4 feet shorter than the recommended minimum height for U.S. zoos.
The city has hired an architect to design a new, more secure pen that would put a 19-foot-tall barrier between visitors and the zoo's big cats, Mollinedo said Wednesday.
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Associated Press writers Paul Elias and Marcus Wohlsen
contributed to this report.
