Noah Berger, Associated Press
Mary Ryan, a San Francisco Zoo employee, arranges a makeshift memorial to Tatiana, the tiger killed by police.

SAN FRANCISCO — Nine days after a tiger mauled three visitors, the San Francisco Zoo reopened Thursday with safety improvements and more signs warning people not to pester animals such as the 350-pound Siberian tiger that killed a teenager.

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.

"We've always felt safe here at the zoo," said Dianne Todd, of Sunnyvale, who was there with her husband and two adolescent sons. The zoo staff, she said, "do their best to keep everybody safe."

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.