A former Marist Brother who abused several boys in his position at a private school in Canberra committed most of the offences he is accused of, but the ACT Supreme Court has been unable to convict him.

Key points: Special hearing was held to determine facts related to abuse

Special hearing was held to determine facts related to abuse 86-year-old Chute is too unwell to attend court or enter a plea

86-year-old Chute is too unwell to attend court or enter a plea Brother Kostka was at Marist College in the 1970s and 1980s

John William Chute, 86, who went by the name Brother Kostka at Marist College in the 1970s and 1980s, was accused of abusing several boys in his care.

But his dementia and Parkinson's Disease have left him too ill to attend court, and unable to enter a plea on the charges.

That meant he was not brought before a jury, and instead faced a special hearing in front of judge David Mossop, to determine the evidence about the charges.

Over several days last week the court heard harrowing details about the abuse of the boys, which often took place on school grounds or in the classroom.

One man told the court he was first introduced to Chute as a boy through a pet Labrador the Catholic Brother kept by his side.

Of the 16 formal allegations made against Chute, Justice Mossop said he accepted that 14 of them had occurred beyond a reasonable doubt.

Prosecutors submitted no evidence for one of the acts Chute was accused of, and in closing submissions Chute's lawyer Greg Walsh told Justice Mossop he would "be satisfied beyond a reasonable doubt as to [most of] the acts".

John Chute (right) was too unwell to attend the hearing. ( ABC News )

Evidence shows Chute groomed his victims

Justice Mossop said the evidence Chute had pursued students was profound.

"The evidence is overwhelming that the accused had a tendency to have a sexual interest in young boys, to whom he obtained access by reason of his position as a Brother in the Marist Brothers religious organisation, and a teacher at Marist College, and to act upon that interest," he said.

"The evidence led in support of each of the charges demonstrates a pattern of conduct that demonstrates a sexual interest in boys in primary or early high school.

"It demonstrates grooming behaviour on the part of the accused in some cases so as to establish a relationship within which acts of indecency could occur."

'It's a terrible thing': Lawyer issues apology

Outside court, Chute's lawyer Greg Walsh issued an apology to the victims.

"I can only say again, as I did in the Royal Commission, even though my client is not fit and he's demented, that there's a sincere apology again to all of the victims," he said.

"The proceedings were difficult and quite stressful and you could see for those complainants who gave evidence the impact of the abuse on them, it's a terrible thing."

Chute's case is one of four that emerged from a police investigation after the Royal Commission into child sex abuse hearings in Canberra.

Mr Walsh said his client could not be charged with many of the crimes until recently, when the statute of limitations for legal action on historic child sexual abuse was lifted.

"Back in 2008 John Chute pleaded guilty to a large number of historical offences, he was sentenced by Justice Gray to a very significant term," he said.

"He was in custody for two years and then another 12 months in periodic detention and then he remained for another three years in an aged care facility.

"If the law permitted it in 2008 a large number of these charges would have been dealt with by way of pleas of guilty.

"But he's been found not fit and so these proceedings have gone along the lines of what's a special hearing."

The court must now decide if a sentence should be imposed, and the case will most likely be referred to the ACT Civil and Administrative Tribunal.