Investigators in Mannheim, in southwestern Germany, have a real whodunnit on their hands, a brutal kidnapping-murder case — but with a twist. The victim is a five-kilogram Humboldt penguin whose lifeless and decapitated body was found last month in a local parking lot.

The gruesome discovery came five days after the animal, of South American origin, was snatched from its enclosure in the Mannheim city zoo. The bird was just 10 months old.

"The case of our missing penguin could not have taken a worse turn," zoo director Joachim Költzsch was quoted as saying by the media outlet Deutsche Welle. "All of us, especially the keepers who have taken care of the animal every day, are shaken. Shattered over its death, but also shaken that someone could have so little respect a living creature."

More troubling still is that the penguin theft isn't an isolated case. Five months ago, 13 lemurs were stolen from a zoo in Thüle, about 50 kilometers west of Bremen. The animal abductors were careful to first disable the facility's security cameras, raising suspicions that it may have been the work of an organized crime ring, the German broadcaster NDR reported.

A year before that, German zoos were hit by a cluster of animal abductions. In December 2015, thieves took two hyacinth macaws — worth tens of thousands of euros on the black market — from Krefeld Zoo, northwest of Düsseldorf. A month earlier, a large King Python disappeared from a zoo in Magdeburg, east of Berlin. And in August of that year, three pigmy marmosets, two green acouchis and two penguins were taken from the Dortmund Zoo, in northwestern Germany, in the space of a few weeks.

The zoo's normally unflappable director, Frank Brandstätter, admitted at the time to being "unnerved" by the abductions. "Because you don't know what will happen next," he told the Munich daily Süddeutsche Zeitung. Brandstätter said 2015 was the "blackest" period of his then 15-year tenure as zoo director, and said he felt like he was trapped in a crime novel, not knowing when or where the culprits would strike next.

Brandstätter believes the thefts are part of an organized animal trafficking racket. "It is a very lucrative business," he said. "Pigmy marmosets are a protected species and they cannot be captured in the wild. Which is why enthusiasts are willing to pay a lot of money for them."

The same goes for penguins, as Brandstätter was told by a sales agent who sells animals to both zoos and private individuals. The animal sales agent said he could sell 100 penguins a day if he wanted so seeing as there's always a demand.

Animal trafficking and smuggling of animal products is the third largest source of income for organized crime after drugs and weapons trafficking, with an estimated annual turnover of $10 billion. And when it comes to the rare-animal market the old rule of "the rarer the animal, the more expensive it is' still very much applies. The 80s saw a thriving trade of birds of prey and rare parrots. Nowadays, one can find animal fanatics in Germany that have callitrichidae monkeys in a cage in their living room, poison dart frogs in their backyard green houses, and crocodiles in the cellar.

But experts assume that in most cases of stolen zoo animals the creatures are trafficked abroad immediately and sold to wealthy individuals for private collections. Insiders cite Russia, China and Arab countries as the top destinations for trafficked animals. Europe is mostly off limits given that animals reared and held in zoos are usually equipped with microchips.

"It's just like how you wouldn't take a stolen Monet to the next available auction house. Instead you'd make sure it is housed out of sight, in a cellar or attic," said Theo Pagel, the director of the Cologne Zoo.