The animals were found on Monday with their abdomens slashed open. A police spokesperson said on Thursday that the authorities are pursuing every possible lead in the case.
Zoo employees are reported to be particularly upset because one of the endangered bears, a three-year-old female, had just reached sexual maturity. Zoo curator Helmut Mägdefrau says it was hoped that she would conceive this year.
Mägdefrau told reporters he has no idea who could have killed the bears.