An experienced 56-year old zookeeper at the Münster zoo in Germany was attacked and killed by a tiger in front of onlookers after forgetting to lock the door to the animal's enclosure. He was pounced on outside of the tiger's compound, The Local reports.

Thursday afternoon, 10-year old Siberian tiger, Rasputin, snuck up on Martin H. during feeding time, where the zookeeper had laid food outside of the enclosure of the compound. Rasputin snuck out of the unlocked back door and jumped on Martin H. from behind, biting his neck and killing him instantly, according to the Westdeutsche Allgemeine Zeitung.

Onlookers witnessed the brutal attack but were not able to call for help in time, although police and the fire department arrived minutes later to the scene.

"An encounter like that with a tiger isn't something that can be survived," zoo chief Jörg Adler said in a press conference on Thursday evening. "There were witnesses, which means we do a reconstruction of the keeper's death. We can install only so much technology and so many alarms - when it comes down to it it's the keeper who decides. It is a tragedy which is hard to comprehend. I cannot describe it."

An investigation is currently underway to determine what caused Rasputin to attack his keeper, though the dominant theory is that Martin H. made a tragic mistake by leaving the door unlocked while placing food down outside, which may have tempted the big cat. Adler added that Martin H. loved his animals, and the zoo will not have Rasputin put down. The tiger was born Leipzig and has lived at the Münster zoo since 2005.

A similar incident occured two years ago in the city of Cologne, when a keeper forgot to shut the door and was killed by a tiger that escaped from his compound.

The latest zookeeper death has prompted animal rights activists to challenge the practice of keeping tigers in zoos. Animal rights group, Vier Pfoten, made a statement following the death of Martin. H, in which they claimed tigers are "incredibly challenging to keep in captivity and potentially extremely dangerous not only for keepers but also for visitors," according to the Westdeutsche Allgemeine Zeitung.

"[Rasputin] sprang on his back as fast as lightning from behind and killed him with a bite on his neck. The zookeeper had no chance. He died immediately," said Dieter Knaack, spokesman for Münster fire service.

Click here to see photos of Martin H., the zookeeper who was killed by Siberian tiger Rasputin. Warning: some of the images may be disturbing to some viewers.