Police are gathering physical evidence trying to reconstruct how and why a 350-pound Siberian tiger escaped and mauled three victims on Christmas day.
A shoe print was found on top of the railing in front of the tiger exhibit, raising questions as to whether a visitor provoked the tiger.
San Francisco Police Chief Heather Fong said, "We also have all three pairs of shoes from the victims and our forensics analysis will allow us to determine if any of those shoes match the print that is on there."
Police say 19 minutes lapsed from the first 911 call to the time the tiger was shot and killed.
Fong said, "[Police] saw a victim seated there on the ground with blood coming from his face. They heard him saying, 'Help me, help me.'"
The first victim was attacked just outside the tiger exhibit and was injured. The tiger then turned its attention to Carlos Souza Jr., also outside the exhibit, and killed him. Then a third victim made a run for the zoo cafe where he was attacked and also injured.
Still, there is still a question about how the tiger got out of its enclosed area. The zoo's director now says the wall separating the enclosure from the public was 12.5 feet high, not 18 feet.
San Francisco Zoo Director Manuel Mollinedo said, "I think the tiger grabbed -- if she grabbed onto something it could have been a ledge … she had to have jumped. How she was able to jump that high is amazing to me but it is an exotic animal."
The zoo said it is adding a fence around all its feline exhibits, installing surveillance cameras and putting in an electrified barrier around all the animal habitats.
The parents of Carlos Souza Jr. said the zoo should have done more.
Carlos Souza said, "How come [the tiger got out]? I want answers."
The two other victims from Tuesday's attack may be released from the hospital in the next two days.