An outgoing member of Fifa's ethics committee says its hands are tied by secrecy within the organisation.

New Zealand barrister Nicholas Davidson QC - one of only six members of the investigatory chamber on the committee - has called it quits.

He says the committee works hard and Fifa investigators are independent.

But he says he found trying to investigate corruption from within the organisation has been frustrating.

Mr Davidson says he was never allowed to see Michael Garcia's 2014 report into corruption in soccer, and he still doesn't know why.

"I'm still guessing, but the answer probably is the fact that the people who received the report would have been looking at it quite quizzically."

He says the organisation may never be free of corruption.

He says once there's criminal activity in an organisation, it is very difficult to totally clean it up.

"You can eliminate people from the game, but that's pretty thin gruel compared with an actual criminal prosecution."