Kingsley Burrell, 29, dialled 999 after being threatened by a group of men while with his young son in Icknield Port Road, Birmingham, on March 27 last year.
But when officers turned up they detained the trainee security guard under the Mental Health Act – despite his family saying he had no history of mental illness.
Within hours Mr Burrell was sectioned and taken to a mental health unit in the city, where his family claim he had mysterious physical injuries and was not allowed to speak to them.
Three days later, police were called to the Mary Seacole mental institute in Winson Green after an “incident” involving the dad-of-two and he was transferred to the Queen Elizabeth Hospital, where he died on March 31.
The Independent Police Complaints Commission immediately launched an inquiry and has now asked Dorset Police to begin a further investigation into the death.
Last night Mr Burrell’s sister, Kadisha Brown-Burrell said the family still had no idea how he had died – and could still be months away from having a funeral.
She said: “How can they keep a body for a year? It’s been more than a year now and they are dragging their heels.
‘‘We are still grieving and need closure but have been told the Dorset Police investigation will take at least take another six months.
“We’re angry and frustrated and don’t know what is happening.
‘‘It’s been painstakingly difficult, frustrating, and emotionally overwhelming for the family to begin to come to terms with his death. Especially, not being able to lay his body to rest, not knowing the sequence of events that led up to his death and how he died.’’
Mr Burrell was dad to five-year-old son Kayden – who was with him when he was detained by police – and 10-year-old daughter Travita.
Student Miss Brown-Burrell regularly visits her brother’s body, which is being held at the mortuary at Sandwell Hospital.
She added: “I personally don’t have much confidence in the IPCC investigation and we have not been kept informed.
“The family has now attended eight or nine pre-inquest hearings, yet still nobody can tell us what or who killed Kingsley.
‘‘It’s not fair on his children, especially his little boy who can’t stop thinking and talking about what happened that day.”
A spokesman for the IPCC said investigators have interviewed four West Midlands police officers under criminal caution and a further 10 officers as witnesses.
He added: “In total, more than 100 witness statements have been obtained from police officers, medical professionals, ambulance staff and members of the public.
‘‘Footage from CCTV cameras at four locations has been recovered and reviewed and hundreds of documents have been seized as part of the independent investigation.
“Earlier this year, after liaison with HM Inspectorate of Constabulary, Dorset Police were requested by the IPCC to begin an investigation into the actions of non-police personnel who had contact with Mr Burrell and they continue to undertake enquiries.
“The IPCC has provided regular updates at HM Coroner’s pre-inquest hearings and to the family and interested parties.’’