(CNN) -- An organization that accredits zoos says the San Francisco Zoo had an "impressive" response to a tiger escape on Christmas Day but could have done more initially, according to a report the zoo released Tuesday.
Tony, a Siberian tiger, relaxes in the remodeled tiger enclosure at San Francisco Zoo last month.
A Siberian tiger got out of its enclosure on Christmas Day, killing a 17-year-old young man and injuring two of his friends, who are brothers. Police shot and killed the tiger.
"The overall response by the zoo to this major emergency was impressive," the Association of Zoos and Aquariums said in an accreditation report the zoo released Tuesday. "There were some exceptions, however."
The association criticized a zoo staffer for doubting brothers Paul and Kulbir Dhaliwal when they said a "'lion was out," putting the staffer and a security guard at risk. The "lion" turned out to be the escaped tiger.
The organization also recommended improvements, especially for the big cat enclosures. The group inspected the San Francisco Zoo on two days in January.
The tiger, Tatiana, apparently scaled a 12-and-a-half-foot wall surrounding her enclosure, attacking and killing Carlos Sousa and injuring the Dhaliwals.
The big cat enclosures were constructed in 1940 and needed updates, according to the report. At the time of the attack, zoo Director Manuel Mollinedo said accreditation inspectors "never noted that as a deficiency" when they visited three years earlier.
In January, association inspectors said they saw construction crews adding a four-foot-high addition to the walls to help keep the big cats in. They said the zoo also provided them with plans for another five-foot extension, with a three-foot overhang to be added.
"These new barriers and the geometry of the adjacent walls appear adequate to contain lions and tigers," the report said. It noted that zoo staff had trimmed back and planned to properly maintain foliage that might assist animals in escaping their enclosures.
The report also recommended minimum staffing levels for the zoo, saying a "majority" of the staff had gone home early to celebrate Christmas when the attack occurred.
"Until this incident, there had not been a visitor fatality resulting from an animal escape at an AZA-accredited zoo," association head Jim Maddy said two days after the attack.
"AZA mandatory accreditation standards require safety and emergency protocols that go beyond federal, state or local requirements," he said. "Regular safety training and annual emergency drills are required by these mandatory accreditation standards." E-mail to a friend
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