Police described it as "terrifying''.
Sheku Bayoh Family Meet Police Watchdog
Relatives of Sheku Bayoh called for ``results rather then broken promises'' after meeting the head of the team investigating his death in custody.
The family of the Fife man told Police Investigations and Review Commissioner (Pirc) Kate Frame that their confidence in the body had been shattered in the weeks following his death.
Father-of-two Mr Bayoh, 31, died after being restrained by officers responding to a call in Kirkcaldy on May 3.
Pirc is investigating the circumstances and will publish a report later.
A post-mortem examination has proved inconclusive and forensic pathology experts have been sought from outside Scotland to help establish the cause of death.
A statement issued by the family's lawyer Aamer Anwar said: "The Bayoh family advised the commissioner Kate Frame that their confidence in Pirc has been shattered.
"Despite an expanded remit, over 17 weeks the Pirc gave an impression of uncertainty about precisely what was being investigated, for what purpose and by what means.
"Today, the family raised questions about the independence and the authority of Pirc; its extremely close relationship with Police Scotland and repeated failures to use its powers or to counter deliberate lies fed into the public domain by police sources.
"The family welcome the Scottish Government's national review of Police Scotland, but if it is to be more than a cosmetic exercise then they cannot afford for Pirc to be seen publicly as a toothless regulator which only serves to whitewash police wrongdoing.
"To this end, the Bayohs respect the commissioner's willingness to meet with them in what was a very robust and difficult meeting to hear their concerns, but if confidence is to be restored they will expect her to deliver results rather than more broken promises.''
The Pirc said last week that all lines of inquiry are being explored to establish the circumstances of trainee gas engineer Mr Bayoh's death.
Police Scotland said they await the conclusion of the Pirc investigation and remain committed to co-operating fully with the body's inquiries.
A collision between an aircraft and a drone was only "avoided by providence'', air investigators have reported.
Heart has discovered cases of the so-called 'zombie drug' Spice are being investigated in Scotland for the first time.
Whyte, 46, is on trial at the High Court in Glasgow, where he denies acquiring the club fraudulently in May 2011.
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