The sister of a man who died after being restrained by police three years ago said her "patience has been exhausted".
Kadi Johnson was speaking at a press conference where Sheku Bayoh's family launched a civil action against Police Scotland for £1.85m.
Mr Bayoh, 31, lost consciousness after being restrained by officers in Kirkcaldy, Fife, in May 2015.
She said police investigations review commissioner Kate Frame should resign.
Mrs Johnson said: "It is three years now since our beloved brother was brutally taken away from us.
"We the family have kept an open mind and had faith in the justice system. But waiting for three years with no answers has been soul destroying.
"PIRC is not fit for purpose. From the start of their so called investigation the aim was to justify the actions of the police and to blame my brother Sheku for his own death.
"The head of PIRC (police investigations review commissioner Kate Frame) failed to approach this investigation openly and fairly.
"We've had enough and our confidence is shattered."
Aamer Anwar, solicitor for the Bayoh family, said the civil action against Police Scotland was unprecedented.
Mr Anwar said: "There has never been a civil action, as far as I know, against the police for a death in custody.
"The family had hoped that by now the Lord Advocate would have made a decision whether he is going to criminally prosecute the police officers concerned or Police Scotland. Three years on and he still hasn't made his mind up.
"The family believe it would be very different if it had been members of the public involved.
"If it had been nine door stewards that had restrained a member of the public, used weapons and that individual dropped down dead, I suspect the Crown Office would not have taken three years to decide if it would end up in a court of law or not."
'He was mistreated'
The family believe the police investigations review commissioner's investigation into the incident was fatally flawed.
The family are suing on the grounds that Mr Bayoh's death could have been avoided.
Collette Bell, Mr Bayoh's partner, said: "It will be three years tomorrow since Sheku was taken from us in a brutal violent way.
"He was mistreated by those that were meant to serve and protect.
"We have always said if Sheku broke the law then the police had the right to act, they did not have the right to perform the role of judge, jury and executioner.
"He will not be forgotten. He will not stop being loved. Would you not continue to fight on?"
A PIRC spokesman said: "The Commissioner appreciates that this has been a difficult period for the family of Mr Bayoh.
"At all stages throughout this independent investigation the PIRC has acted under the direction of the Lord Advocate who has ultimate responsibility for the investigation of deaths in Scotland.
"The PIRC conducted an extensive and detailed investigation into Mr Bayoh's death.
"More than 500 statements were obtained by PIRC investigators who also gathered evidence from a wide range of experts, including those suggested by the Bayoh family and their legal representatives, to give a greater understanding of events leading to Mr Bayoh's death.
"The Commissioner submitted a report to the Lord Advocate in August 2015.
"A further report containing evidence gathered from a number of expert witnesses was submitted in August 2016 and the PIRC has undertaken any additional enquiry requested by the COPFS (Crown Office and Procurator Fiscal Service)."
'Further work to do'
A Crown Office spokesman said: "We recognise that this has been a difficult time for the family of Sheku Bayoh. The family, and their legal representative, have been kept informed of any significant developments and senior Crown Counsel along with Crown Office officials met recently with the family and will continue to do so where appropriate.
"This has been a complex and challenging investigation and while there is still some further work to do, considerable progress has been made in the last few months.
"It is not appropriate at this stage to commit to any timescales given the nature of the investigation. However, it's anticipated a full report will be submitted for the consideration of Crown Counsel, the most senior lawyers in the Crown Office, in due course."