A Canadian judge deciding on David Bain's compensation claim was paid nearly $400,000 for his report.
The Government asked retired Canadian Supreme Court Justice Ian Binnie to assess Mr Bain's claim for wrongful conviction and imprisonment last November.
He delivered his report to Justice Minister Judith Collins early in September.
Justice Binnie was paid almost $315,000, excluding GST, for his work on the report, and nearly $34,000 for travel and other expenses, according to documents released to Radio New Zealand under the Official Information Act.
He travelled to New Zealand four times over 11 months to speak with Mr Bain and people involved in his two trials.
The Ministry of Justice says he was paid $450 an hour - comparable to what a New Zealand Queen's Counsel is paid when determining compensation claims.
Justice Binnie's bill could rise further if the Ministry of Justice receives more expense receipts from him.
Mr Bain was convicted in 1995 of murdering his parents, two sisters and brother in Dunedin, but his convictions were quashed by the Privy Council in 2007 on the grounds a substantial miscarriage of justice had occurred, and a retrial was ordered.
He was acquitted at the retrial in June 2009, and lodged a claim for compensation with former justice minister Simon Power in March 2010.
The Government is refusing to confirm reports Justice Binnie has recommended he be compensated for his 13 years in prison.
Cabinet is yet to decide whether to pay Mr Bain compensation.
The Government is under no obligation to pay compensation, but according to the formula used in its last compensation payment, Mr Bain stands to receive about $2 million for loss of liberty and livelihood, and emotional harm.