Killer tiger 'may have been freed on purpose'

The big cat exhibit at San Francisco Zoo was cordoned off as a crime scene today as investigators probed whether a 21-stone Siberian tiger that killed a visitor escaped from its high-walled pen on its own, or was let out deliberately.

Police shot the animal on Tuesday after a rampage that began when the tiger escaped from an enclosure surrounded by what zoo chiefs said were an 18ft wall and a 20ft moat. Two brothers who were also visiting the zoo were severely mauled.