A suspected robber has died after he was restrained by members of the public and then handcuffed by police.
The Independent Police Complaints Commission (IPCC) is investigating after the man in his 30s went into cardiac arrest and died later in hospital.
Police were called to reports of a suspected personal robbery in Holloway Road, north London, at around 10.45pm on Thursday.
Officers found a man had been detained by members of the public.
A Scotland Yard spokesman said: "The man, aged in his 30s, was handcuffed by police but not placed under arrest and was identified as being unwell."
London Ambulance Service were called and the suspect was taken to hospital where he died shortly after 12.10am on Friday.
The Met's Directorate of Professional Standards attended the incident which has been referred to the IPCC. The police watchdog will investigate the contact police had with the dead man, Scotland Yard said.
Detectives believe they know the identity of the man and next of kin have been informed but he has yet to be formally identified. A special post mortem is due to take place.
Officers from the homicide and major crime command are investigating the circumstances of the man's death. An incident room has been opened at Lewisham police station.
A London Ambulance Service spokeswoman said: "We treated a man in cardiac arrest and made extensive efforts to resuscitate the patient. He was taken as a priority to hospital."