The officers had breached their duty of care and had ignored pleas by witnesses and Mr O'Brien that the arrested man could not breath, Nigel Sweeney, for the prosecution, told the jury at the Old Bailey. Mr O'Brien, who weighed 19st, was held face-down on the ground, with his hands held behind his back by two handcuffs, then carried to a van by six officers, he said.
Police Constables Richard Ilett, 34, Gary Lockwood, 33, and James Barber, 29, all deny the charge of manslaughter.
The court was told that Mr O'Brien, of East Dulwich, south London, went to a christening with his partner Alison and their two sons on Easter Sunday, 3 April, 1994. They then went to a dance at an Irish community centre in Walworth.
Police were called to the venue at about midnight, after a disturbance broke out. Mr O'Brien and his family had taken no part in the disturbance and left the hall to wait for a lift outside, Mr Sweeney said. But PC Ilett arrested Mr O'Brien - who was then uninjured - for being drunk and disorderly, said Mr Sweeney.
The officers took him across the road where he ended up face down with two sets of handcuffs placed on him.
Mr Sweeney said the officers had used "extensive, unreasonable and therefore unlawful force, holding him down for a prolonged period".
Mr Sweeney said: "Mr O'Brien died because he could not breathe as the result of them holding him face down on the ground. Mr O'Brien also sustained 31 areas of injury during the arrest, including a number of lacerations to the face which bled profusely."
In statements, the officers had outlined their positions as they held the man down. PC Ilett said it had been with one knee in Mr O'Brien's back and at some stage holding his head so that he did not injure himself.
PC Lockwood said he restrained the man's middle and legs. PC Barber held Mr O'Brien's lower legs against his thighs.
Mr Sweeney continued: "Holding a fat man in that position meant that, because of his size, his stomach was pressed against his diaphragm, restricting his ability to breathe."
Mr O'Brien was placed face-down in the van and did not move or make a sound during the short journey to the police station, said Mr Sweeney.
At just after 12.30am he was carried into Walworth police station in south London, where attempts were made unsuccessfully to revive him.
The trial, which is expected to last six weeks, was adjourned yesterday while the jury was taken to Walworth to view the main locations involved in the case.Reuse content