A child sexual abuse victim of Hillsong founder Brian Houston’s father Frank has questioned the “audacity” of Scott Morrison continuing to support Houston, and the possibility Houston may have been invited to accompany the prime minister to the White House in September.

Frank Houston, who died in 2004, headed the Assemblies of God church in New Zealand until the early 70s, while Brian was the head of the Australian branch from 1997 until 2009, and founded Hillsong in 1983.

Frank was accused of sexually abusing nine boys, and in 2015 the royal commission into institutional responses to child sexual abuse found Brian had failed to report his father’s abuse to police.

One of Frank’s victims, Brett Sengstock, has since waived his anonymity provided by the commission. He was raped by Frank in the 60s and 70s, and gave evidence to the royal commission under the pseudonym AHA.

Sengstock has repeatedly questioned why Brian failed to alert police to his father’s crimes when Frank Houston confessed his guilt in 1999.

In an interview on Channel Ten’s The Project on Sunday, Sengstock said it was “shocking” that Morrison, after becoming prime minister, would go on stage with Houston at Hillsong. Morrison addressed the opening session of the church’s annual conference in July.

“I couldn’t believe the audacity. Here’s the prime minister of this country on stage with Brian Houston [who] is currently under investigation by New South Wales police for concealing the crimes of his father, and up there with their arms around each other. I am absolutely lost for words.”

Last month US media reported the White House vetoed one of Scott Morrison’s guests for Donald Trump’s state dinner. This raised lots of questions, which still haven’t been answered. 1/2 pic.twitter.com/ivcXdzpkt2 — The Project (@theprojecttv) October 27, 2019

Last month the Wall Street Journal reported that Morrison wanted Houston in his entourage for the state dinner with US president Donald Trump in September, but the White House shot down the idea.

In an interview with 2GB host Ben Fordham on Thursday, Brian Houston said Sengstock told Houston he did not want the police informed, at the time the church leader found out about his father’s abuse.

“He told me that he didn’t want the police involved,” Houston said. “And the reality is that the law itself actually spells out that very circumstance – that if an adult victim doesn’t want the police involved, that’s a reasonable excuse for not including the police.”

Speaking to the New Daily later on Thursday, Sengstock denied he had said that.

Houston told Fordham the investigation remained open only because no charges had been laid, and until that happened it would always be open.

NSW police have confirmed that the investigation remains open with the Hills area command, but declined to comment further.

The royal commission referred Brian Houston to NSW police because he did not report his father’s abuse to police.

In Houston’s submission to the commission, he makes it clear he believed at the time that Sengstock did not want to report the matter to police.

Houston told the royal commission at the time that because Sengstock was an adult it was “his prerogative” to report it to police, and he did not want it reported. Houston’s lawyers at the time argued if that were not a “reasonable excuse” as defined in law, than others, including Sengstock and his mother, were also potentially in breach of the law.

Houston confronted his father in November 1999 and said he suspended his father from preaching. He claimed Frank “never ever preached anywhere again” after that.

In December 1999, the national executive of the Assemblies of God decided that Frank Houston’s credentials would be withdrawn.

But evidence given to the commission showed Frank Houston was allowed to resign from his position in the church in 2000 and retire with financial support from the church “without damage to his reputation or the reputation of Hillsong Church”.

Frank’s letter in November 2000 stated he was resigning “as I feel it is time for Hazel and I to enter retirement”.

In a December 2001 letter to ministers of the church marked “extremely confidential”, the church’s vice president, Keith Ainge, laid out the reasons for Frank Houston’s departure and the “great anguish” it was causing Brian, and warned ministers not to speak publicly about it.

“We cannot see any reason for this to be announced to your church or further afield. Sadly there are always one or two people with their own agendas who will try and get mileage from other people’s pain,” Ainge said.

The church admitted it didn’t follow some of the procedures required at the time, and the royal commission found that Houston had a conflict of interest in heading the organisation as it handled the complaints investigation against his father.

The Newcastle Herald reported last week it had obtained a recording from 2004, the year Frank died, that showed Frank giving a sermon at a Maitland church.

In that sermon, Frank can be heard referring to an eight-year-old boy as “good looking”.

Hillsong has said it will sign up to the federal government’s $4bn national redress scheme established after the royal commission, but has yet to do so.

The prime minister refused to say whether Houston’s name was put forward for the White House state dinner. The finance minister, Mathias Cormann, also declined to answer in Senate estimates last week.

Officials raised concerns that providing information on who was put forward on a list of potential invitees could “prejudice international relations”.