A man who died after being detained by police appeared to be "fragile" and "there was no need" for how he was treated by officers, an inquest heard.
Leon Briggs, 39, died in November 2013 after being detained under the Mental Health Act at Luton police station.
Witness Lauren Billington said she saw a man shouting "help" and "get off me" as he was held down by a group of officers in Marsh Road, Luton.
She said she felt "distressed like I wanted to help him".
Father-of-two Mr Briggs was held by Bedfordshire Police under section 136 of the Mental Health Act, which gives officers the power to take a person of concern from a public place to one of safety.
He was placed in a cell at about 14:25 GMT on 4 November. He became unconscious and was pronounced dead in hospital at about 16:15.
The inquest heard the lorry driver's primary cause of death was "amphetamine intoxication with prone restraint and prolonged struggling".
A secondary cause of death was given as coronary heart disease.
The inquest heard Ms Billington was being driven in a car by her then husband and they slowed down to see what was happening on Marsh Road.
It was just a few seconds, but she said she could see Mr Briggs being held on the floor by a group of officers with their backs to her, next to the wall by a shop, the court heard.
She said in her police statement her first thought was she "did not think it was necessary for three men to restrain one very skinny man".
The court heard that a pathologist is set to describe Mr Briggs as a man of "muscular" build, who was 6ft 1in (185cm) tall and weighed 15 stone and 4lbs (97kg).
Ms Billington told the inquest: "I remember feeling like there was no need for whatever that was going on. To me he just seemed fragile and there was no need for how they were going on with him."
Ms Billington said she could "remember my feelings about it better than what I actually saw".
She had earlier seen Mr Briggs when she was in a carpet shop, and told the jury: "It was clear to see that he was mentally unstable or there was something going on."
Ms Billington later read about the incident in a newspaper and accepted in court that "maybe" she had been shocked by the report rather than what she had seen.
The inquest continues.