The massacre came in two parts: zookeepers found nine of the birds dead in their enclosure on Friday, and another six Saturday. Both attacks occurred at night.
Despite placing extra-security on duty after the first attack, the zoo's director Manfred Niekisch said the birds do not typically cry for help and the guards were unable to prevent Saturday's killings.
Niekisch added that autopsies of the birds have yet to reveal whether the killer was human or animal. Bite marks on the bodies indicated a fox may have been responsible, though they may have occurred after the flamingos were killed.