A convicted prisoner told an inquest that he heard a schizophrenic patient screaming as police used shields and sticks to restrain him in his cell.
Matthew Costello told the jury at Windsor Coroner's Court he was detained at Slough police station when Giles Freeman was placed in a cell nearby.
Mr Freeman, 37, was taken to the police station on 15 October, 2002, after "lashing out" at his mother.
According to police, he was given a sedative but died shortly afterwards.
The inquest heard earlier this week that Mr Freeman was brought in and placed in the cell for an emergency mental health assessment so he could be sectioned.
But after a struggle, including at one point where the court heard that Mr Freeman had "rugby charged" the cell door, he was injected with a sedative.
Shortly afterwards Mr Freeman turned "blue" and was taken to Wexham Park Hospital where he was declared dead.
On Wednesday Costello, who admitted he was a "crack head" when the incident happened, told the inquest how he had been trying to sleep in his cell when Mr Freeman arrived in the early hours of the morning.
Costello said: "I heard the banging, I heard the sticks and the shields, I heard people being put on the floor, I heard the screaming and shouting then everything went quiet.
"When I came out of my cell all of their kit was lined up, about five shields."
He was cross-examined by Andrew Warnock, representing Thames Valley Police, who said: "There were no shields used."
But Costello replied: "You are messing this up now saying I didn't see things."
Costello admitted in court that he had taken heroin a few hours before his arrest and asked if he had been high at the time, he said: "Yes, I suppose so."
Mr Warnock continued: "Is your recollection of this not very good?"
But Costello replied: "Good enough, I remember what I need to remember."
Asked what he thought of the police in general, he replied: "Scum, that's my personal view."
The inquest continues.