The police watchdog is to investigate the death of a 29-year-old man who had "contact" with West Midlands Police.
Kingsley Burrell was detained under the Mental Health Act on 27 March after officers attended an incident on Iknield Port Road, Birmingham.
He was admitted to a unit in the city and later moved to a hospital where he died on 31 March.
The Independent Police Complaints Commission (IPCC) said a post-mortem examination had been conducted.
Died in hospital
But a spokesman said they were still waiting for the results of further tests.
An inquest is due to open and adjourn at Birmingham Coroner's Court on 12 April.
Mr Burrell, who was from the Hockley area of Birmingham, died at the Queen Elizabeth Hospital in Birmingham after being taken ill the previous day.
The spokesman said as he had had a number of interactions with police over the previous four days, West Midlands Police had informed the IPCC on 30 March that Mr Burrell was in a serious condition in hospital.
He added Mr Burrell was being treated at the Mary Seacole Mental Health Unit, in Birmingham, on 30 March when staff at the unit had called the police for assistance to help deal with a disturbance involving Mr Burrell.
Following this, Mr Burrell was taken to the Queen Elizabeth Hospital for treatment to a cut above his eye before being discharged to the Oleaster centre, in Birmingham.
Officers were involved throughout and remained at the centre before leaving.
'Robust independent investigation'
While at the centre Mr Burrell suffered a "serious medical condition" and was transferred to the Queen Elizabeth Hospital where he died on 31 March.
The IPCC has met with Mr Burrell's family to explain the investigation.
Investigators will look at how police officers responded and dealt with Mr Burrell, including any use of restraint, as well as considering the protocols between the force and the mental health trusts.
IPCC commissioner Rachel Cerfontyne said: "The IPCC appreciates the need of Mr Burrell's family, and the communities affected, to get answers to the questions they have about his death.
"I can assure them that I will oversee a robust independent investigation that sets out to find out what happened in the police dealings with Mr Burrell."