His courage in coming forward last year indeed prompted other subjects of Stephen James Porter's crimes to speak to investigators, exposing more than a decade of sex offending.

Porter, 51, is now awaiting sentencing in the ACT Supreme Court, having pleaded guilty to four charges linked to the abuse or grooming of three boys and the possession of child exploitation material.

The court must deal first with a factual dispute in relation to the most serious charge, which is that Porter maintained a sexual relationship with a boy for about three years from 2015 until 2018.

Crown prosecutor Andrew Chatterton alleges Porter engaged in sexual activity with this child up to 40 times, while Porter's barrister, Jack Pappas, argues there were no more than 15 such occasions.

The number of times a particular type of sexual activity took place is also a topic of controversy.

The court began, on Thursday afternoon, to watch a video of an interview this victim did with police just prior to Porter's arrest in mid-2020.

The rest of the roughly three-hour-long discussion was played for Justice Chrissa Loukas-Karlsson on Friday, when the victim was seen to describe what Porter did to him as "an abomination".

"It's not godly," the boy told police.

He spoke of being in shock throughout many of the incidents, during which he would stare at the ceiling or close his eyes to avoid seeing what was happening.

The abuse began after Porter, a Macgregor man who coached at the Ainslie Football Club, approached this victim's parents and initiated a private Australian rules mentorship arrangement.

A year or so went by without any inappropriate behaviour, according to the victim, who indicated unwanted advances eventually became a regular thing.

"I always felt like I had to do it," he said in the video.

"It was just part of doing training, and [sexual contact with Porter] was just what happened afterwards."

The boy told investigators the abuse occurred at both Porter's home and his own, with at least one incident happening on one of his birthdays.

He detailed how Porter was, aside from during their unlawful sexual contact, like an uncle to him, leading him to feel a sense of loyalty that influenced his decision to stay silent about the abuse for years.

"I felt ashamed about the whole thing," the boy said.

"I didn't know if people would believe me because of how close [Porter] had gotten to my family."

After what he described as an internal "battle", the boy disclosed the abuse to a church pastor who helped him tell his parents.

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He spoke to police about a fortnight after this, telling investigators Porter had described engaging in sexual activity with other boys.

The victim was also aware that Porter was, at that time, still coaching children.

"That's part of the reason I came forward, because who knows who else he's doing this to," he told police.

Once the video had finished, this victim gave evidence under cross-examination by Mr Pappas.

He denied "simply inventing some of [his] answers", but he conceded he may be mistaken about some details.

"It's hard for me to recall specific dates and times," the victim told the court.

Porter is set to give evidence when the disputed facts hearing resumes on a date yet to be determined.

The 51-year-old remains on bail.

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