Footage showed Mr Tomlinson apparently being pushed by an officer - video courtesy Guardian.co.uk
The family of a man who died at the G20 protest say it has been painful to watch video footage of him being shoved to the ground by police.
Newspaper seller Ian Tomlinson, 47, died of an apparent heart attack in the City of London on 1 April.
A criminal inquiry into the death began when video footage later emerged showing him being shoved by an officer minutes before he collapsed.
His stepson Paul King spoke as hundreds joined a silent march in his memory.
The demonstrators, dressed in black, gathered in Bethnal Green Police Station in east London and walked to the spot where Mr Tomlinson died near the Bank of England.
Footage shown on Channel 4 News, appears to show a policeman hitting Mr Tomlinson with a baton, and another video clip obtained by The Guardian newspaper appears to show an officer shoving him to he ground.
The Independent Police Complaints Commission (IPCC) is investigating the death of Mr Tomlinson.
The police officer filmed in in the footage has been suspended after coming forward.
"We are still coming to terms with his tragic death under such tragic circumstances," Mr King, 26, said before the march began.
"We are hopeful that the IPCC will fulfil their duty to carry out a full investigation into his death and action will be taken against any police officer who contributed to Ian's death through his conduct.
It was a miracle no one else was killed
Protester David Mellows
"The developments of the past week, particularly the footage shown of Ian, have been painful to watch."
The family did not join the march, but Mr King thanked the protesters and appealed for a peaceful demonstration.
Some protesters have suggested they could remain in the city until Sunday.
A notice on the G20 Meltdown website said: "Some of us may feel strongly like staying at that place until Ian Tomlinson and his family get justice."
Mark Barrett, a supporter of the march and organiser of the G20 Meltdown, said: "Our hearts are with the friends and family of Ian Tomlinson and we can't possibly imagine what it must feel like for them.
"We do feel strongly that we must all work together - police, people who command the police and the protest movement - to make sure something like this never happens again."
David Mellows, who took part in the G20 protest, harangued police officers posted outside the station over their colleagues' behaviour that week.
"The only violence I witnessed that day was police violence," he said.
"It was a miracle no one else was killed."
LOCATION OF IAN TOMLINSON AND G20 PROTESTS IN CITY OF LONDON
1. Protests at Bank Junction
2. Protest outside RBS branch in Threadneedle Street
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