The details of the incidents in early July at the Dutch island have emerged through questioning the teenage suspects, who revealed they found their inspiration online, the Osnabrück state prosecution office in Lower Saxony said.
“There they found instructions for anal sex practices,” spokesman Alexander Retemeyer said.
So far videos of the crimes have not appeared on the internet, but police are monitoring the situation, he added.
The suspects, up to 13 youths between the ages of 14 and 15, have shown remorse for their actions during talks with police, spokesperson Georg Linke said.
“They apparently had no clue about how they were making the victims feel,” Linke said. “The boundary between play and criminal acts were not perceptible for them.”
The attackers allegedly used objects including cola bottles and broomstick handles to sexually assault six boys, all aged about 13. The incidents occurred at the youth dormitory of a holiday camp sponsored by the city of Osnabrück's municipal sports association.
According to state prosecutors, terrible scenes of violence occurred there when the older boys pulled the youngest and weakest members of the 39-member group from their bunks and assaulted them in the centre of the room.
Some of the victims may also have been among the alleged perpetrators, Retemeyer said.
The entire group will be questioned throughout their summer vacation, after which the camp supervisors – some of whom are suspected of failing to intervene – will be questioned.
The mother of one of the victims contacted police in early July, after which police were able to quietly conduct their investigation for 10 days. But now the media frenzy over the alleged crimes has created major obstacles in continued work on the case, police said. Some parents had cancelled their children's interviews with police due to media attention, they added.
The incidents have led to a debate about the need to improve supervision at summer camps. The Lower Saxony state sporting federation has already announced it will examine further measures for training of supervisors.