BERLIN, Jan. 2 (Xinhua) -- Three women allegedly responsible for a fire in a zoo in German city of Krefeld have turned themselves in to the police, representatives of the police and public prosecutor's office announced on Thursday.

They said the cause for the fire, which devastated the monkey house of Krefeld Zoo in New Year's Eve, has been identified.

The three women, aged between 30 and 60, confessed to having launched five sky lanterns which are believed to have started the fire that killed more than 30 animals, German authorities said during a press conference.

The public prosecutor's office was now investigating into the 60-year-old mother and her two adult daughters for negligent arson, the German authorities confirmed.

Sky lanterns are made of paper and heated with a candle or fire paste. It ascends to the sky through the generated heat. After causing a deadly fire which killed a boy in 2009, it has been illegal in Germany to launch sky lanterns.

According to the investigators, the women ordered five sky lanterns on the internet and there was no indication on the packaging that they were banned.

During the press conference, the investigators said that the three women had expressed "several times" that they were very sorry about what happened.

Around 36 hours after the deadly blaze in the monkey house, chief inspector Hoppmann said police had received many clues and the case was "largely resolved" although tests with comparative material were now planned to investigate why the fire was spreading so quickly.

A sprinkler or fire alarm system was not installed in the monkey house because this was not mandatory at the time of construction in 1975.

According to the Krefeld Zoo, the two chimpanzees who "miraculously" survived the devastating fire were being cared for by several zoo veterinarians.