Britain's independent police complaints body is stepping up an inquiry into the death of a man during protests against the G20 meeting in London last week and has requested a second post-mortem.
The Independent Police Complaints Commission opted to take over the inquiry from City of London police and make it fully independent after footage emerged showing Ian Tomlinson, 47, a newspaper seller, being shoved to the ground by an officer.
Mr Tomlinson was not involved in the demonstrations and was on his way home from work when he became caught up in clashes between police and protesters last Wednesday in a street close to the Bank of England.
The video footage was filmed by a New York fund manager who was in London on business and shown on the Guardian newspaper website.
It shows Mr Tomlinson shuffling slowly along with his hands in his pockets as riot police and dog handlers close in to clear the street.
One officer appears to lunge at Mr Tomlinson from behind, pushing him with enough force to send him sprawling on the ground. He is then shown sitting up and apparently remonstrating with the officers, before bystanders help him up.
Minutes later he collapsed in a nearby road and died from what Home Office pathologists say was a heart attack.
Additional video footage released late on Wednesday, this time from Channel 4 news which covered the protests, appeared to show an officer striking him with a baton in the moments before he was pushed to the ground.
Mr Tomlinson's family are demanding answers and Home Secretary Jacqui Smith has called for a quick and thorough investigation.
The investigation will look into whether contact with officers contributed to his death.
"People are rightly concerned about this tragic death and this footage is clearly disturbing," said IPCC deputy chair Deborah Glass.
Several officers identified in the footage have come forward.
Opposition politicians in Britain have called a criminal investigation. The commission says all its investigations consider whether criminal offences have been committed.