A man who has accused a Canberra Marist Brother of abusing him decades ago says he reported his abuse to police but was turned away because officers believed the brothers would not do such a thing.

Key points: John Chute is facing 16 charges stemming from his time as a Marist Brother

John Chute is facing 16 charges stemming from his time as a Marist Brother The court hears the accuser went to police, but was turned away

The court hears the accuser went to police, but was turned away The court will hear from several witnesses

The man is a witness in the case against 86-year-old John William Chute, also known as Brother Kostka, who is accused of abusing six boys in the 1970s and 1980s.

He appeared by video link to his nursing home in Sydney because he is too sick with Parkinson's disease and dementia, and has been ruled unfit to plead.

He has been excused from further participation in the hearing, which began on Tuesday after a last-ditch attempt to permanently stay the charges was rejected.

The witnesses reported the abuse from about the age of 12, and described a series of incidents in Mr Chute's office, the playground and while others were present in the classroom.

Two of the former students described the ageing, white-haired teacher as like Father Christmas, and told the court the teacher sometimes abused them on a daily basis.

One of the men said he went to police to report his sexual abuse, but was turned away by officers who said the Marist Brothers would not do such a thing.

"I've never been able to trust anyone since this time," he said.

"I feel broken."

The man described how Mr Chute would come to class wearing a cassock with no underwear and commit indecent assaults on him while pretending to talk about schoolwork.

He told the court he saw the same thing happen to others, but kept his head down, fearing that making eye contact would mean he would be next.

"I started to feel grossed out," he said.

The man said he finally hit out during an incident at a school theatre night, when after an indecent act, he stood up and smashed his head against the wall repeatedly to stop the attack.

He said he also kept saying "leave me alone", but it was to no effect.

"There was never the opportunity to tell him to stop, he was a Brother," he said.

Mr Chute is facing 16 charges including indecent assault and one charge of buggery.

The ACT Supreme Court is still to hear from three other witnesses, as well as evidence from experts in the treatment of child sex abuse.