The former Australian Border Force commissioner Roman Quaedvlieg has personal knowledge of the involvement of Peter Dutton’s office in the unusual ministerial intervention in a foreign au pair’s visa case, a source has told the Guardian Australia.

The visa status of the two unknown young women has been in the spotlight since March, when it was revealed the former home affairs minister used his discretion powers to grant them visas on public interest grounds.

Dutton stood aside as a minister on Monday after challenging Malcolm Turnbull for the leadership of the Liberal party.

Speculation is mounting that he could launch another challenge by the end of the week.

Quaedvlieg, who was sacked from his role in March after a nine-month investigation into allegations he helped his girlfriend get a job at his agency, could be about to weigh in to the saga with new information.

Guardian Australia understands from a source close to Quaedvlieg that he has personal knowledge of the involvement of Dutton’s office in one of the cases.

Quaedvlieg is reportedly examining Hansard records to ensure the responses the minister and department provided are consistent “with the facts as he knows them to be,” the source said. “He has personal knowledge of the involvement of Dutton’s Office in the ministerial intervention”.

The source said that if Quaedvlieg found the facts were inconsistent with his own account, he would consider seeking to correct them. So far he has not alleged any such inconsistency.

In the first case, an au pair whose visa was cancelled at Brisbane’s international airport in June 2015 was able to make a phone call and within a couple of hours Dutton approved a new visa.

In November the same year, Dutton defied written warnings from his own department that granting a visa to a second au pair was of “high risk” because she had previously been warned about work restrictions.

Dutton has previously insisted he doesn’t know the two au pairs and they didn’t work for his family.

“For the wider record, I do not personally know the individuals concerned nor does my wife. They have never been associated with us in any way. We have never employed an au pair,” he said in March.

“There were two young tourists who had come in on a tourist visa and declared … [they] intended to perform babysitting duties while here. The decision that was taken, I was advised, was that the tourist visas would be cancelled, that those two young tourists would be detained and that they would be deported. I looked into the circumstances of those two cases and I thought that inappropriate.”

Dutton has refused to answer specific questions about the identity of the au pairs’ employers.

Earlier this month, the Guardian Australia revealed Dutton’s department had spent $10,000 in taxpayer cash fighting a legal battle to keep documents secret about the au pair visa decisions.

The department has said that it was unable to calculate the number of cases with similar circumstances in which travellers have been allowed to stay in Australia despite suspicions they would undertake paid work.

“Determining the number of times this has occurred would require an examination of a large number of individual cases and an unreasonable diversion of departmental resources,” the department said.

The department insisted the identity of the person/s who made representations to the minister or his office on behalf of the au pairs was not a matter for the department.

Comment has been sought from Dutton.