The Express newspaper group said angry critics began making threats against zoo director Theo Pagel, going so far as to publish his home address.
"The attacks on the social network have reached a level that we cannot expect our employees to tolerate," zoo executive Christopher Landsberg said.
Pagel shot and killed tiger "Altai" after he escaped and attacked the 43-year-old identified only as Ruth K. on Saturday - to allow rescue workers to reach her faster.
Tranquillizing the tiger would have taken too long, said Pagel, who called it "the darkest day of his life."
Colleagues and police defended his decision.
"One had to assume after the attack that the zoo keeper was still alive," Frankfurt Zoo director Manfred Niekisch told HR radio on Monday. "Our colleagues in Cologne had no other choice."
But it appears she died almost certainly died immediately, a spokesman for the public prosecutor said on Tuesday, as the tiger bit her on the neck, severing her spine, according to preliminary autopsy results.
There was no indication of drugs or alcohol in her blood which might have affected her judgement.
The prosecutor said it remained unclear why she was in the same area as the nearly 300-kilo animal. She was an experienced keeper, and had worked at the Cologne zoo since 1990.
It wasn't the first time she was attacked. In 2005, she was attacked by a Persian leopard, the Express reported, which left her with bad scars on her neck.