Head of the Ex-Border Force sends more evidence to Dutton's au pair investigation

The former Border Force commissioner Roman Quaedvlieg has provided more material to the inquiry into au pair visas.

The former head of the Australian Border Force who accused Peter Dutton's chief of staff of asking for help for "the boss's partner" is presenting more evidence before a Senate committee.

Ex-ABF commissioner Roman Quaedvlieg sent a letter to the Senate committee alleging that Mr. Dutton's chief of staff, Craig Maclachlan, requested help in June 2015.

Mr. Dutton has labeled the letter "completely false and even fabricated" and says that Mr. Maclachlan did not work for him until October 2015.

Mr. Quaedvlieg has now sent additional information to the Senate committee, which is investigating Mr. Dutton's use of his ministerial powers to uproot two au pairs from immigrant detention.

"I will not comment publicly in the media about the details of my supplementary presentation, except to state unequivocally that the effective substance of my original submission is valid," Mr. Quaedvlieg said in a statement on Friday.

In an explosive rebuttal to Mr. Quaedvlieg's evidence, Mr. Dutton questioned the mental health of the former border chief and said he resented losing his job for misconduct.

Mr. Quaedvlieg was dismissed from his post after helping his girlfriend get a job at the Sydney airport.

"I urge Dutton to desist from personal attacks and slander about my actions, motivation, integrity, reputation and mental health," Quaedvlieg said.

With a report due on Tuesday, Labor Senator Murray Watt believes that another public hearing is needed to get to the bottom of the saga.

"These latest revelations and contradictory evidence mean we need to have another audience," he told ABC radio.

"It's very typical of Peter Dutton, when he's under pressure, to start throwing mud at other people."

The minister of the cabinet, Mathias Cormann, said that the allegations of the former head of ABF contained inaccuracies of facts.

"Mr. Quaedvlieg is obviously not a credible witness," Senator Cormann told Sky News.

Mr. Dutton voided his department's decision to deport a woman in June 2015 and was granted a visa to remain in the country, despite his original plans to work for a former colleague of the Queensland Police of Mr. Dutton.

Dutton faces questions about whether he cheated on parliament by saying there was no personal connection between him and his former police colleague.

He has said that he had not spoken to his former police colleague for 20 years, but the man called his office for help with the au pair case.