A man who was detained under the Mental Health Act has died in hospital after his condition deteriorated at a police station.
The Independent Police Complaints Commission (IPCC) is investigating Surrey police following the death of 33-year-old Terry Smith.
The ambulance service requested police help just after 10pm on Tuesday after being called to an address in Stanwell, Surrey.
Smith was held under the Mental Health Act and taken to Staines police station where he was then arrested on suspicion of a drugs-related offence. His health deteriorated and he was taken from the station by ambulance to St Peter's hospital in Chertsey, where he died at around 9pm on Wednesday.
IPCC investigators were carrying out house-to-house inquiries on Thursday and distributing leaflets in the Douglas Road area.
After being told about the incident just after 6am on Wednesday, investigators went to Staines police station to assess evidence, including CCTV from the custody suite where Smith was held, and they also took initial accounts from those involved.
IPCC commissioner Jennifer Izekor said: "Our investigation is in its very early stages and our thoughts and condolences are with Terry's family and friends. What we have established is that Surrey police were called by an ambulance crew to assist them with dealing with a man just after 10pm on the evening of Tuesday 12 November.
"Within 20 minutes of their arrival they detained Mr Smith under section 136 of the Mental Health Act, and he was then taken to Staines police station. Our investigators have seized and viewed CCTV footage from the custody suite where Mr Smith was detained and restrained. At some point Mr Smith became seriously ill. An ambulance was called and took him to St Peter's hospital.
"I would urge anyone in the Douglas Road area who witnessed any of the events of Tuesday evening to get in touch with us, as it could really help our independent investigation. We have met with Mr Smith's family to explain our role and how the investigation will progress."
Smith was described as white and about 5ft 8in and was reported to be acting strangely.
Witnesses can contact the IPCC on 0800 096 9073.
