A Dutch father who is accused of holding captive his six unregistered children in a bunker allegedly told them that "bad spirits" would enter their bodies if they talked to any outsiders - one of many disturbing and bizarre allegations that surfaced in court this week.

Gerrit-Jan Van Dorsten, who did not attend the pre-trial hearing Tuesday in Assen, the Netherlands due to health reasons, is charged with unlawful detention, child abuse, sexual abuse, and money laundering, the BBC reports.

Police found the 67-year-old man and his five adult children in the isolated farmhouse -- stowed away in the basement through a staircase that was hidden behind a cupboard in the living room -- during an October raid after a sixth child, 25, escaped to a local pub in the village about 80 miles north of Amsterdam.

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“All the children report physical punishment if they were deemed to be under the influence of spirits. This happened from a very young age, with children as young as four or five years old,” prosecutor Diana Roggen told the judges, Reuters reported.

“The punishments would consist of beatings, sometimes with a stick or other objects, pulling off their hair, sometimes making them sit in a cold bath for hours. Sometimes they were choked to the point where they became unconscious.”

Since 2007, Van Dorsten withheld food, drink, or medical treatment, and some of the older children said their father forced them to perform sex acts on him after his wife died in 2004, prosecutors said. He blamed his wife's death on his children, the prosecution said.

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He would also tell his children “a female spirit, the spirit of their mother or another spiritual wife” had entered their bodies to justify sexual acts with them, Roggen said.

One of the children was tied up by his hands and feet as punishment, while another was forced to spend the summer in the doghouse at 12 years of age, prosecutors told the hearing.

Never registered or attending school, the youngest six of Van Dorsten's nine children "lived in seclusion from birth, were kept indoors and had to be quiet so that no-one would notice that they existed", prosecutors noted.

While the eldest four children, three of whom had left home and the 25-year-old man who raised the alarm, support the criminal case against their father, the younger five siblings - who are currently in counseling - stand by their father, according to a statement given to a Dutch filmmaker working on a documentary about the odd case.

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“We have learned from our father to seek happiness in your relationship with God and to take your education into your own hands and we still believe in that,” they said in the statement.

In October, the Family Federation for World Peace and Unification, also known as The Unification Church, told Fox News that Van Dorsten "was briefly a member of our movement in the mid-1980s," but added that he "is known to have suffered from mental health issues and left our organization in 1987.

It has been reported that in 2014, he suffered a stroke that was left untreated and has rendered him unable to speak.

A second suspect, Austrian Josef Brunner, 58, a follower or accomplice of Van Dorsten who paid the rent on the farmhouse, is charged with endangering the health of others and unlawful detention, according to Reuters.

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Brunner called the trial a "witch hunt," adding he "did not rob anyone of their freedom."

Fox News' Travis Fedschun, Samuel Chamberlain, and The Associated Press contributed to this report.