Transport Ministry fraudster Joanne Harrison had a business partner who got a 30 percent cut of stolen money and shredded fake invoices when an investigation was launched - but was never charged.

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Harrison was sentenced in February to three years and seven months in prison for defrauding the ministry of more than $700,000.

After months of delays the Transport Ministry has finally released a report it commissioned into Harrison to RNZ News.

The employment investigation by Peter Churchman QC reveals that Harrison had a business partner, a former public servant at the ministry, who acted as a front person for fake companies - Mazarine Associates and Elizabeth Williams Consulting.

Documents previously released by the Transport Ministry show between August 2014 and March 2016 Harrison authorised payments of $499,223 to the two companies.

Harrison's business partner, whose name is being withheld by the ministry, told investigators that Harrison, a general manager at the ministry, convinced her that Harrison was now working as a contractor for the ministry and was legitimately billing it for her time.

Peter Churchman, who is now a High Court judge, found the business partner had been "groomed" by Harrison while at the Transport Ministry and "misled" about the businesses they were setting up but also treated her statements with "considerable caution".

"On one view of the matter, she would appear to have been a party to a fraud carried out by Joanne Harrison and to have received 30 percent of the funds paid by the Ministry to Mazarine Associates and Elizabeth Williams Consulting where those entities had no lawful basis to receive those funds," Mr Churchman wrote.

"She may have been attempting to shift blame on to Joanne Harrison and portray herself as a completely innocent party."

WhatsApp Chat messages that were uncovered from Harrison's phone by a separate Deloitte investigation and are included in Mr Churchman's report have revealed a conversation between the pair - when they were both aware a Transport Ministry investigation was underway.

Harrison's business partner wrote:

"Remind me! How did you think this would be a good idea!

"Remember at the start it was going to be legit...I found some of the original invoices in your writing...amounts for the month etc yesterday...shredded now."

Joanne Harrison urged her to "stick fast".

"So I need you to stick tight, play it cool or even annoyed at being asked. I'm gonna be history in spectacular style so you can keep ya distance."

In a statement to RNZ News the Transport Ministry said its former employee believed "they were collaborating on legitimate contracted work for the Ministry" and that "this person appears to have been intentionally deceived by Harrison".

The ministry said Harrison's business partner co-operated with the Serious Fraud Office and no charges were laid.

"The Police worked with this individual to recover funds that were received through the work they undertook with Joanne Harrison."

Mr Churchman's report also found Harrison had "groomed" another Transport Ministry worker who then attempted to interfere in the fraud investigation on her behalf by attempting to enter her office and remove items.

This worker also planted a letter in the payroll office in attempt to trick the ministry into believing Harrison's husband had done work for the organisation.

"I find that this conduct amounts to serious misconduct," Mr Churchman found.

The report also reveals Harrison tricked three government agencies - the Transport Accident Investigation Commission, Worksafe and the Transport Ministry, into employing her husband Patrick Sharp, without ever disclosing they were in a relationship.

Firstly, she tricked the Transport Accident Investigation Commission into hiring him, but Mr Sharp abruptly quit when staff became suspicious he was in a relationship with Harrison.

Mr Churchman's report shows Harrison then convinced Worksafe to hire Mr Sharp - telling them he was one of the Transport Ministry's "top investigators".

But after just a couple of weeks Mr Sharp threw a "tantrum" and quit his new job at Worksafe when he was not given a company vehicle.

Harrison then got a him a job as a writer at the Transport Ministry but he never turned up or did any work.

In August, the Auditor-General Martin Matthews resigned from his position following a critical report into how he handled the fraud case when he led the Transport Ministry.