A former youth worker and foster carer who sexually abused three boys in his care about 20 years ago will be sentenced next week.

A former youth worker and foster carer who sexually assaulted three teenage boys more than 20 years ago was allowed to leave Western Australia despite one of his victims complaining about the abuse, a Perth court has heard.

Roderick Alexander Finch, 55, has pleaded guilty to 21 child sex offences including indecent dealings with a child, sexual penetration of a child and attempted sexual penetration of a child.

The Perth District Court heard on Thursday that Finch was the foster carer for two boys – one of whom was classified as having “special needs” – who he plied with alcohol before sexually abusing.

The third victim, a 16-year-old boy, was a juvenile offender who was abused while doing community work at a camp.

The court heard Finch moved to Queensland in the 1990s despite one of the boys complaining to police about him.

Since there had been no other allegations against Finch at the time, the only way to charge him was to extradite him, which was not warranted for one charge of indecent dealing, the court heard.

Finch’s lawyer, Jeremy Noble, said his client was not evading authorities.

“He has genuine and extreme remorse,” Mr Noble said.

Referring to the pre-sentence report, Mr Noble said Finch admitted he had “destroyed” his victims’ lives but also noted that he only offended over a period of about two years.

In a letter to his lawyer, Finch said: “I can only pray for forgiveness from the court, from God and the innocent victims.”

“I had the chance to help these kids and I didn’t help them at all – I damaged them.”

Mr Noble outlined Finch’s own traumatic past including sexual abuse and a car accident that left a young girl dead.

Finch, who has suffered two strokes in the past four years, has also been convicted of possessing child pornography and is currently fighting similar charges in Queensland.

Prosecutor Mark Nicol said Finch’s abuse demonstrated an ongoing breach of trust.

Judge Felicity Davis remanded Finch in custody and told him an immediate prison sentence was inevitable.

Outside court, one of Finch’s victims, Rob McAuley, said he was disappointed the sentencing had been delayed until February 7 but was pleased Finch had been remanded in custody.

“I’m actually happy – at least he ain’t going anywhere,” he said.

The 36-year-old said he only found out about the other victims about six months ago and it was difficult for him to sit in court as details of the abuse were read out.

“I tried not to break, which I didn’t, but I had to walk out and catch my breath for a while,” Mr McAuley said.

He said he would like Finch to apologise to him personally and said he still thought about the abuse “almost every day”.