The Assassin of the Wild Animals

At the Budapest Zoological Garden, the keepers are in turmoil. An unknown torturer has taken cruel joy in murdering wild animals for several days. One morning a hippopotamus was found dead and poisoned pellets had been thrown into it. The next day three crocodiles had their eyes gouged out with stones. Then an ostrich died from eating a cake full of pins.
Just one clue. A bloody finger was found in a lion's cage. The king of the desert did not fall for the murderous madman's offers.