‘All of us are shocked, numb, totally gutted,’ said an angry Samantha Rigg-David outside Brixton police station on Saturday following the death in custody of her brother, Sean Rigg.
The family are demanding answers into how mentally-ill 40-year-old Rigg, from Balham, died.
Rigg was held on suspicion of assaulting a police officer and public order offences near Atkins Road, Brixton, south London, on Thursday.
He fell ill and died 90 minutes later.
The Independent Police Complaints Commission (IPCC) is carrying out an investigation.
Police had still not formally identified Sean Rigg on Saturday and have yet to reveal the results of his post-mortem examination.
The family laid flowers outside Brixton police station on Saturday.
Rigg-David said of her brother: ‘He had a mental illness but he was very fit. From the time of arrest to the time of being brought into police custody, he collapsed and died.
‘We’ve not been told why. We are being upright as a family and we have come down here ourselves to find answers.
‘All of us are shocked, numb, totally gutted. We are anxious, some of us are very angry.’
The IPCC said in a statement on Friday: ‘The Independent Police Complaints Commission has launched an independent investigation following the death of a man in police custody in Brixton last night (Thursday 21 August 2008).
‘At approximately 7:15pm yesterday, police were called to reports of a man whose behaviour was causing concern to members of the public in the Atkins Road area, SW12.
‘Officers went to the scene and a 40-year-old man was arrested on the neighbouring Weir Road on suspicion of public order offences and assault on police. He was taken to Brixton police station.
‘At approximately 8.15pm, while he was in the holding area of the station, the man became unwell. A doctor, who was already present at the station, examined the man.
‘An ambulance was called and he was taken to King’s College Hospital where he was pronounced dead at 9.24pm.
‘The Metropolitan Police Service referred the incident to the Independent Police Complaints Commission. Three IPCC investigators were deployed to the scene and worked throughout the night.
‘The IPCC has secured CCTV from the custody suite and local area. Investigators have also identified a number of significant witnesses who are currently being interviewed.
‘An IPCC Family Liaison Manager has been appointed and is currently in contact with the man’s family.
‘A post-mortem will be carried out later today to establish the cause of death.
‘IPCC investigators are seeking witnesses and will be in the Weir Road area this evening, 24 hours on from the incident, handing out leaflets and speaking to members of the public to appeal for witnesses.
‘IPCC investigators believe they know the identity of the man, but await formal identification and confirmation that next of kin has been informed.
‘The man is described as black and as being bare-chested and wearing white trousers.’
l The IPCC confirmed yesterday the man was Sean Rigg.