The tiger escaped from its enclosure at Cologne zoo on Saturday, police said. It made its way over to an adjacent building where it attacked its 43-year-old keeper. She later died in hospital of her injuries.
Investigators said the enclosure had not been properly locked, allowing the feline to get out.
The tiger was put down by zoo director Theo Pagel immediately after the attack.
"Today is the darkest day of my life," Pagel said.
He added that visitors to the zoo in the German state of North Rhein-Westphalia were at no point in danger. Police had briefly cleared the area after the incident. It later reopened for visitors.
Cologne Zoo was founded in 1860 and is one of the oldest and best-known in Germany. It's home to some 10,000 animals from 700 species.
ccp/kms (dpa, AFP, AP)