The Serious Fraud Office won't pursue criminal charges against former Waikato District Health Board chief Dr Nigel Murray over his alleged misuse of public money.

SFO director Julie Read said committing additional "very high level of resources required to prove criminal charges beyond reasonable doubt was not in the public interest".

Read said it would have required extensive investigation in Canada and the public interest did not warrant that cost given the amounts allegedly obtained.

Murray resigned in October 2017. A State Services Commission inquiry released in March 2018 showed he spent $218,000 on travel and accommodation in the three years he held the $560,000 job, half of which was either unauthorised or unjustified.

The case was referred to the Serious Fraud Office (SFO).

In a statement today, Read said the SFO concurred with the conclusions reached by the SSC about Murray's conduct.

"The SSC investigation found that Dr Murray's conduct did not meet the minimum standards expected of him as a CEO in the State sector, and that more than half of his travel and accommodation expenses were unauthorised or unjustified.

"The matter was referred to the SFO to investigate whether there had been any wrongdoing of a criminal nature."

A damning DHB investigation into the irregular expenses, released to the Herald under the Official Information Act last year, showed:

• Murray already had his relocation costs from Canada extended from $15,000 to $25,000 when he spent more than double the agreed amount.
  • He personally booked a $1617 international flight for a woman from San Francisco to Auckland using taxpayer money.
  • He spent two nights in Las Vegas during a trip to the United States on virtual health business. On the same trip, which he later largely refunded, Murray went to Canada for seven nights.
  • He booked a rental car in Moncton, Canada for two months despite only being in the city for six days.

According to the draft report, Murray booked the flight from San Francisco to Auckland for the woman, whose name was redacted, by telephone to the DHB's agent Tandem Travel on May 15, 2017.

This circumvented the usual process which was for the chief executive's assistant to book travel.

It also breached his employment contract because all travel was supposed to be agreed and authorised by then board chairman Bob Simcock, and no personal travel for himself or family and friends was allowed.

A the time, Murray's lawyer, Calum Cartwright of Cullen Law, said the report was never concluded.

"The excerpts you have received are only [the author's] draft findings and were subject to change following any comment from Dr Murray.

"Dr Murray had many concerns about the investigation and its draft findings, which were not addressed in the draft report because the investigation was stopped."

It was stopped when the board agreed to Murray's resignation.