In a case with echoes of the Fritzl family horror in Austria, Ondrej Mauerova was partially skinned in the closet in a cellar at his home in Kurim near Brno, in the Czech Republic.
The abuse – involving members of a religious cult – was uncovered by chance last May when a neighbour's television baby monitor picked up graphic pictures of what was happening next door.
Ondrej and his nine-year-old brother Jakub were locked and chained in the cellar for months by their mother Klara, 31 – a member of a group called the Grail Movement.
He was caged, beaten and gagged to stop him screaming, according to reports.
Mauerova had the monitor installed so that she could watch the abuse from her kitchen but the images were picked up by a neighbour who used an identical system to monitor a newborn baby, the regional court in Brno has heard.
Police were called and the two boys as well as what appeared to be a 13-year-old girl were freed.
But the girl later turned out to have been one of the alleged abusers, 34-year-old Barbora Skrlova.
She subsequently fled to Norway before being brought back to the Czech Republic earlier this year.
Mauerova has admitted abusing her children but she said she had been manipulated by Skrlova and her own sister Katerina.
The accused are Klara Mauerova, her sister Katerina, 34; Barbora Skrlova, 33; her brother Jan Skrla and a friend Jan Turek.