Gerd Hoppmann of the Krefeld criminal police told a press conference Thursday that the suspected perpetrators reported themselves to the authorities and that it can be assumed that they are the ones that caused the zoo fire.
"For us, the case is largely cleared up," said Hoppmann, adding that the women were accused of negligent arson.
Investigators said that handwritten messages were found on sky lanterns near the damaged area.
A short history of German zoos
More than 70 million people visit tigers, tapirs and toucans in Germany each year. But modern zoos are nothing like the "storage cells" for animals of days gone by. Here's a look back.
Image: picture alliance/blickwinkel/K. Hennig
The pandas are coming!
Trees for climbing, an artificial river, species-appropriate plants - preparations for Chinese pandas Jiao Qing (pictured) and Meng Meng have been in high gear at Berlin's Zoological Garden. The Panda Plaza is now up and running after the two arrived on a first-class flight from China June 24. Such luxury for animals has not always been the case. Here's a look back at the history of German zoos.
Image: picture-alliance/dpa
Germany's first zoo
Professor of zoology Martin Hinrich Lichtenstein was so enthused with the Zoological Garden in London that he wanted to build one himself. In 1841, he was able to convince Friedrich Wilhelm IV to do it. The King of Prussia decreed that some 22 hectares (54 acres) be sectioned off from Berlin's Tiergarten and turned into Germany's first Zoological Garden.
Image: picture alliance/dpa/arkivi
The first animals move in
By 1845, two coatis, three Arctic foxes, a red jackel, two badgers, 24 monkeys, and three bears from Siberia were living there. In 1846, lions and tigers were moved into their own building. The first elephant came onto the scene in 1857, in 1861 the first zebra. Yet sadly, there was a high animal mortality rate.
Image: picture alliance/dpa/arkivi
Vienna as a role model
The Schönbrunn Zoo in Vienna took a completely different and much grander approach. In 1906, the first elephant to be conceived in a zoo was born. By 1914, Schönbrunn was one of the largest zoos in the world, with 3,500 animals from 717 species. It became a role model for the Berlin Zoo. Today, Schönbrunn is one of the oldest existing zoos in the world and allegedly the most visited in Europe.
Many zoos sprung up in German-speaking countries in the second half of the 19th century. After Berlin, Frankfurt, Cologne, Hamburg, Basel, and Leipzig followed suit. But Prussian King Wilhelm IV had already created his own wildlife park back in 1571, which he used not only for hunting - he also allowed nature researchers to live there.
Image: picture-alliance/dpa/P.Pleul
Building conservation versus animal preservation
Many compounds, such as this Antelope House in Berlin's Zoological Garden, were built in the 19th century and attempted to reflect the exotic origins of the animals. But as aesthetically appealing as they may have been, they were not always species-appropriate. Still, they cannot be altered because building conservation laws stand in the way.
Image: picture-alliance/dpa/dpaweb/B. Setnik
Education and relaxation
In the 20th century, zoos popped up all over Germany, and aquariums opened up as well. Monkey parks, ocean parks and bird parks became a craze, and people could even drive their cars or take the bus through safari parks. With the economic boom of the 50s and 60s in Germany, even smaller cities could open zoos or animal parks.
Image: picture-alliance/dpa/F. Leonhardt
Rage in the machine
Post-war Germany saw a boom in zoos, with people eager to witness exotic animals. Zoos became living classrooms, but a remotely species-appropriate way of keeping the animals wasn't a priority. Cages and trenches separated lions, tigers and elephants from visitors. It wasn't until the 1970s that research revealed more insight into the psychology of animals, and zoos began altering their designs.
Image: picture alliance/blickwinkel/K. Hennig
Back to nature
A milestone in zoo design are panorama areas such as the one Carl Hagenbeck built in Hamburg. Rather than being stuck in cages in a systematic way, animals are kept according to "continents." Lions live near zebras, giraffes, and elephants, for instance, in the "Africa" region of the zoo. Green zones at the Cologne Zoo (pictured) ensure that animals are kept similarly to their natural habitat.
Image: DW/Nelioubin
The future of zoos
Small cages and concrete pens are becoming more and more a thing of the past. Yet how zoos develop in the future depends on smart management. Some zoos, such as in Frankfurt, for instance, have decided to close their elephant houses. As a small zoo in the inner city with just 11 hectares (27 acres), it simply could not provide the animals with enough space.
Image: picture-alliance/dpa/P. Zinken
Zoo research
Zoos breed species and aim to return them to the wild. They are also involved in environmental conservation and educate visitors about their habitats. But zoo opponents say that to keep certain animals species alive only in zoos is unethical. Instead, focus should be placed on keeping their natural habitats intact. Pictured is a newborn platypus named Mackenzie.
Zoos in Germany get more visitors than sporting events. Nowadays, they're more like entertainment parks with adventure playgrounds, themed restaurants and merry-go-rounds. A little farm at the Cologne Zoo recently opened, where visitors can pet cows and goats. Zoos are now irreplaceable, not only for visitors to reconnect with nature, but also to preserve certain endangered animals.
Image: Picture-Alliance/dpa/P. Steffen
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The women said several times they were "infinitely sorry" for the fire, according to the investigators.
Hoppmann said the women ordered the sky lanterns online and did not know they were banned. He also praised the fact that they had come forward voluntarily as "very courageous."
If convicted of negligent arson, the suspects face a fine or imprisonment of up to five years.