The Independent Police Complaints Commission is appealing for witnesses to an incident in Exeter city centre earlier this week, which it is investigating.
A man was arrested by local police - he later became unwell while in custody and was taken to hospital with head injuries.
Police were called to reports of a disturbance at the junction of the High Street and Paris Street shortly before eleven o'clock on Wednesday morning.
A 32 year old man was restrained by several officers, and arrested on suspicion of a public order offence - concerns later developed for his health.
The IPCC is asking anyone who saw what happened in the street to get in touch - they say the man was in dark clothing with a baseball cap and glasses, and is believed to have spoken to several people shortly before his arrest.
Investigators are also viewing CCTV footage ofthe area and the police custody suite.
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