Newspaper vendor Ian Tomlinson was unlawfully killed by PC Simon Harwood
at the G20 protests in London, an inquest jury has ruled.
Criminal proceedings could reopen against the Scotland Yard officer after jurors ruled he acted illegally, recklessly and dangerously in shoving Mr Tomlinson to the ground.
PC Harwood used "excessive and unreasonable" force in hitting Mr Tomlinson with a baton, the jury said. Mr Tomlinson posed no threat, they added.
Evidence from PC Harwood and pathologist Dr Freddy Patel was discredited as part of the verdict which will prompt reviews by both the Crown Prosecution Service and the Metropolitan Police.
Mr Tomlinson, a homeless 47-year-old newspaper seller, collapsed and died on the fringes of the demonstrations in central London on April 1, 2009.
The death became an international controversy after New York businessman Christopher La Jaunie handed footage he had taken of the police confrontation to the Guardian newspaper.
Prosecutors said last year that a decision not to pursue charges against PC Harwood could be reviewed in the light of the inquest's findings.
Dr Patel's claim that Mr Tomlinson died of a heart attack was discredited by the jury in favour of a string of experts who said he died of internal bleeding.
PC Harwood was accused by the victim's family of telling lies in a bid to get off the hook.
Mr Tomlinson had been turned away from a line of officers with his hands in his pockets when PC Harwood hit out.
CCTV images, police helicopter footage and hand-held video recordings show Mr Tomlinson cutting a lonely figure as he staggered away from a police cordon after being hit with a baton.
Footage shows Mr Tomlinson gesturing to police and appearing angry after being sent tumbling to the ground.
He eventually collapsed flat out and muttered "they got me, the f****** got me" before dying minutes later.
Scotland Yard colleagues were shocked by PC Harwood's actions. PC Kerry Smith said: "He (Mr Tomlinson) sat up and looked towards us and he said 'I just wanted to go home'."
Appearing for three days at the hearing in Fleet Street, central London, PC Harwood apologised to family members for "any way" he may be responsible for the death.
But relatives' lawyer Matthew Ryder QC said he told "half truths" and "deliberately painted a false picture of Mr Tomlinson".
The barrister added: "I am going to suggest to you that you are not here to help Mr Tomlinson's family but to help yourself."
Mr Tomlinson, who was born in Matlock, Derbyshire, was an alcoholic with a series of medical complaints who had slept rough for 20 years.
Dr Patel initially found the death was consistent with natural causes because the newspaper seller had coronary artery disease and could have died at any time.
But another two pathologists, Dr Nat Cary and Dr Kenneth Shorrock, later carried out their own post-mortem examinations and came to a different conclusion.
Dr Cary suggested that Mr Tomlinson could have been pushed so he fell with his right arm trapped under his body, hitting his liver and causing it to bleed internally.
Widow Julia said the death devastated her family, adding: "I remember feeling he was the best thing that ever happened to me."