A man who was arrested for theft offences has died in police custody.
The 46-year-old was found dead in his cell on Monday at about 07:00 BST. He was arrested on Sunday night and taken to Elland Road police station in Leeds.
The Independent Police Complaints Commission (IPCC) has launched an inquiry into his death.
The IPCC said: "Any death in custody is a very serious matter and we have begun an independent investigation to determine the full circumstances."
Officers arrested the man on an outstanding warrant at Leeds General Infirmary, where he had earlier been taken after a report from a member of the public.
He was taken to the police station and put in a cell but when officers checked on him, he was found unresponsive and pronounced dead, despite attempts to resuscitate him, the IPCC said.
Results of a post mortem examination on Tuesday proved inconclusive and further tests are being carried out.
The IPCC said it was gathering initial accounts from police officers and recovering CCTV footage from the custody suite.
West Yorkshire Police said it was investigating the circumstances of the man's movements prior to him being found and taken to hospital.