Three women who flew paper sky lanterns to celebrate the New Year are under investigation after a zoo fire in Krefeld, Germany, killed dozens of animals and burned down a primate enclosure, the police said Thursday.

In a statement, the North Rhine-Westphalia Police Force in Krefeld said the women, a mother and her two adult daughters, came to them and said they had let five sky lanterns loose on New Year’s Eve.

Officers had been able to secure four sky lanterns near the primate enclosure, the police said in their statement. The missing fifth lantern was “almost certainly” what started the fire, it added. The women are being investigated on suspicion of negligent arson.

The Krefeld Zoo said on its Facebook page on Wednesday that the fire had gutted the enclosure, calling it an “unbelievable tragedy.” Hours later, the zoo said only two apes in the enclosure had survived and were slightly injured.