Police have refused to release a report on the fatal shooting of James Ashley, saying it would be too expensive.
James Ashley was shot at close range by police in January 1998
Sussex Police said files on his death in 1998 contain 30,000 pieces of paper, which would cost £3,000 to photocopy.
Mr Ashley, 39, from Liverpool, was in bed when police entered his flat and shot him after incorrect intelligence reports suggested he might be armed.
Louise Ellman, MP for Liverpool Riverside, said the force's decision was "totally unreasonable".
Police said although the request, made under the Freedom of Information Act, was turned down there was a right to appeal.
Mr Ashley was naked and unarmed when police shot him in the chest, but three senior officers were cleared in 2001 of wrongdoing in the raid at the St Leonard's flat.
The shooting of Mr Ashley led to the chief constable at the time, Paul Whitehouse, resigning.
The costs of releasing the file would also include lawyers' time to examine the papers to work out which sections could be released.
But Ms Ellman, who has campaigned on behalf of the Ashley family, said the decision not to release the report was "very disappointing".
She said: "There are exclusions under the Freedom of Information Act on what information can be made available but in this case I think it is totally unreasonable.
"After all, it's now agreed that James Ashley was killed in an entirely unjustified situation.
"Given that background, I think it is amazing that there is a refusal to publish those reports which talk in more detail about what happened and who was responsible."
A spokesman for Sussex Police said the force was unable to reveal who made the request.