BERLIN -- A Siberian tiger attacked and killed a female keeper at Cologne zoo on Saturday before being shot dead.
The gate of the tiger's enclosure had not been properly shut, allowing the big cat to jump on the woman and maul and bite her, a zoo spokesman said.
The director of the zoo, Theo Pagel, shot the tiger from a rooftop, the spokesman added. Police briefly cleared the area after the incident but the zoo later reopened for visitors.
The victim's name was not immediately released but she was said to have been 43 years old.
"This is the darkest day of my life," Pagel later said in a brief statement at the zoo's entrance, the Kolner Stadt-Anzeiger news website reported.
"I shot and killed the animal so that we could enter ... and take a look. But the employee was already dead," he added.
"We cannot yet explain how the keeper could make such a fatal mistake (of failing to close the gate)," Pagel said.
The Cologne zoo in western Germany, founded in 1860, is one of the oldest and best-known in the country.
Reuters contributed to this report.