Mr Toogood was asked by the State Services Commission to find out how the letter reached Prime Minister Helen Clark's electorate office, from where it was sent to the Beehive.
In his report, he said it was not sent to the electorate office by immigration officials and he also cleared Helen Clark's office staff of any responsibility.
Immigration Minister Paul Swain said he was pleased the inquiry cleared his department's staff, and Helen Clark told NZPA she was pleased the "false and damaging" allegations against the service and her electorate office staff had not been substantiated.
However, National Party MP Judith Collins, who persistently raised the issue in Parliament, said she was not satisfied with the report.
"It confirms my belief that the terms of reference for this inquiry were always going to be too narrow, and the findings leave many questions unanswered," she said.
"The actions of ministers and their staff, including those who leaked the guinea pig letter to the media, were conveniently excluded from the inquiry."
Ms Collins said she thought that restricting the terms of reference was a deliberate attempt to keep the full details from being made public.
"If the Government had been serious about uncovering the truth, it would not have tied the hands of those doing the investigation from the very start," she said.
Ms Curtis was also unhappy with the report.
She did not agree with conclusions over how the letter reached Ms Dalziel.
"I believe that Mr Toogood did his best with the information that he had. Unfortunately he didn't have enough information," she told National Radio.
"I am really concerned that the Immigration seems to have walked out of this without any blemish whatsoever."
Mr Toogood had not spoken to her client, who was interviewed in Sri Lanka by a staff member from the New Zealand High Commission in New Delhi.
She insisted her client had never had the guinea pig letter copied.
- NZPA
Christopher Toogood QC:
Report for the State Services Commissioner on Inquiry Into Actions of Employees of the Immigration Service and the Parliamentary Service
re leaking of the "guinea pig" letter to the media [PDF]
