KIRK HARGREAVES/The Press
The Government has been criticised for its handling of Canadian Judge Ian Binnie's report, which is believed to recommend compensation.
But Collins said today she did not take the decision lightly to have it peer reviewed.
Bain is seeking compensation for wrongful conviction and imprisonment over the 1994 killings of his parents, brother and two sisters.
In a statement today, Collins she referred Judge Binnie's report to the Solicitor General because of concerns after reading it.
"My concerns are broadly that the report appeared to contain assumptions based on incorrect facts, and showed a misunderstanding of New Zealand law. It lacked a robustness of reasoning used to justify its conclusions.
"This was not a decision I made lightly, but one that was absolutely necessary. Put simply, it would not be acceptable to make a recommendation to Cabinet based on a report that would not withstand the considerable scrutiny it would attract.
"I am very disappointed this peer review is needed - I think we would all agree that a timely conclusion to this matter would be best for everyone. But justice must be done - a robust and proper process is the only way to ensure a certain and final conclusion to Mr Bain's claim.
"When the Secretary for Justice and I met with Justice Binnie in September, I made it clear to Justice Binnie there were concerns with the report he provided, and it would be peer reviewed.
"I also advised Justice Binnie the report must remain confidential and it would be premature to release it until after Cabinet had made a decision on Mr Bain's claim.
"Since then, I have received from Justice Binnie, unsolicited, two further versions of his report.
"I will receive Mr Fisher's peer review in the next day or so, which will be forwarded to Justice Binnie for his comment. When I hear back from Justice Binnie, I will take a recommendation to Cabinet on the next steps."
The review would not have an impact on Bain's claim, other than to delay it, Collins said.