In the case before the regional court in the western city of Münster, four men and a woman accused of complicity are in the dock.
They are suspected of grievous abuse of children including the then 10-year-old son of the girlfriend of the 27-year-old main defendant, a computer technician.
He is believed to have trapped two boys in a garden shed in April this year
along with several male accomplices, drugged them and sexually abused them
repeatedly over the course of three days. Prosecutors say they have 30 hours
of video evidence.
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The chief defendant's mother, a 45-year-old woman who owns the shed, is believed to have been aware of the abuse and is charged with aiding and abetting it.
Investigators said they had identified at least three victims, aged five, 10 and 12 years old at the time.
The defendants are among 11 people arrested in the case, with at least 22 other people under investigation. The trial is expected to last until February.
It is just one of a series of horrific child abuse cases to rock Germany this year, prompting a tightening of legislation.
In June, investigators said they were probing some 30,000 suspects as part of a probe into a “deeply disturbing” online paedophile network linked to the city of Bergisch Gladbach.
In an earlier scandal in Lügde, 125 kilometres from Münster, several men abused children hundreds of times at a campsite over a period of a number of years.
Last month, the German cabinet agreed tougher punishments for using and sharing child pornography with the maximum prison sentence for offenders to
increase to 15 years from 10.
“Offenders fear nothing more than being discovered,” said Justice Minister Christine Lambrecht, whose ministry drafted the law.
“We must therefore massively increase the pressure to prosecute, and the
terrible injustice of these acts must also be reflected in the level of penalties.”
The draft law also bans sex dolls with a childlike appearance, introducing
fines and jail sentences for anyone who owns, produces or distributes them.