Corrective Services Minister Joe Francis has made a formal apology to a senior West Australian bureaucrat as part of a defamation case settlement.

In March, Mr Francis publicly blasted the then Department of Corrective Services (DCS) chief financial officer George Kessaris, saying he had been "caught out for incompetence".

The attack came after an internal memo Mr Kessaris wrote revealing significant "governance concerns" were leaked to the media.

The memo, to the Office of the Auditor General, outlined a litany of financial waste and mismanagement at WA's prisons, including $51 million being tacked onto an already approved annual budget without authorisation.

The ABC understands an internal DCS investigation could not determine who was responsible for the leak and Mr Kessaris denies it was him.

At the time, Mr Kessaris had refused to sign the DCS 2014-15 financial reports over feared breaches of the Financial Management Act and accounting standards.

At a press conference after the memo was leaked, Mr Francis blamed Mr Kessaris for the financial discrepancies.

"The CFO of the department ... for that particular financial year was responsible for all the expenditure of the DCS and I find it amazing that he wouldn't sign off on his own work ... which is one of the reasons he is no longer the CFO," Mr Francis told journlaists.

Settlement confidential

Mr Kessaris sued Mr Francis for defamation and the case was recently settled out of court, including a formal apology by Mr Francis and a confidential financial payout.

In the apology, written on Ministerial letterhead, Mr Francis said he "unreservedly" apologised "for any harm my statements may have caused".

Mr Francis would not say who had paid the financial settlement. ( ABC News: Andrew O'Connor )

"I also accept the decision to transfer you from the position of CFO of the DCS to another position in the department was a mutual decision and not intended to be, or regarded as a demotion of your position with the department," Mr Francis wrote.

Mr Francis would not answer any questions about the settlement including if the money had come from him personally, the Liberal Party or the taxpayer.

"The matter has settled on confidential terms to the mutual satisfaction of the parties," he said in a statement.

But Mr Kessaris said it was "disturbing" that more effort was spent on investigating who leaked the document than focussing on its contents.

'Traumatic and devastating': George Kessaris

He said it had been an "horrific" year for him and his family.

"It's been very traumatic and devastating. It's affected me personally, my family, my health has suffered, wellbeing. My ability to return to workplace has been shot," he told the ABC.

"I felt abandoned by my employer, I felt targeted. It has damaged my reputation, it damaged my name. I was feeling totally betrayed."

Mr Kessaris said he was not a whistleblower because he was simply doing his job by alerting the senior executive to significant issues.

"I followed the legislation, I followed the ethics and the professionalism expected of a chartered accountant," he said.

He said his career in government appeared to be finished.

The DCS has had Mr Kessaris on 'garden leave' since September, which means he sits at home on full pay (a package worth around $180,000) while they find him a suitable role.

"As a taxpayer and personally I find that very hard to reconcile. Particularly for someone like me who has always worked, and I want to work and I want to contribute," he said.

In a statement, DCS said it had made an offer of "ongoing support" to Mr Kessaris.

The Opposition's spokesman for corrective services Paul Papalia said Mr Francis had many questions to answer over the financial settlement, and owed Mr Kessaris a public apology, "not a cowardly one sent by a letter".

"Clearly a settlement has been made — did the taxpayer pay for that settlement? If so, that sounds improper to me," he said.

Mr Papalis said Mr Francis should investigate the issues of financial incompetence raised by Mr Kessaris in his leaked memo, instead of focusing on a "witch hunt" into the source of the leak.

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