The 43-year-old member of staff at the zoo was attacked by the tiger and suffered such severe injuries that she died shortly after being taken to hospital.
It seems Altai, an adult male tiger managed to get out through a security tunnel which was not properly secured and into an administration building.
This building was not open to the public, but there was a window open there, through which the big cat could have got out and into the open.
The zoo was evacuated as police moved in, even using a helicopter to ensure they could maintain an overview of what was happening.
Meanwhile zoo director Theo Pagel managed to shoot and kill the tiger through an opening in the administration building roof.
“This is the darkest day of my life,” Pagel told reporters afterwards.
“The zoo director has the right weapons for such a task,” a police spokesman said, adding that the police service pistols would not have been much use against a tiger. “Our guns would not have even scratched it,” he said.
Founded in 1860, Cologne zoo is one of the oldest in Germany. It has around 10,000 animals of more than 750 species, and welcomes around 1.4 million visitors a year.