The police officer thought to be shown in video footage of the G20 protest in London pushing a man who later died has come forward.
An independent criminal probe has begun into the death of Ian Tomlinson, 47, who had a heart attack minutes later.
Additional video footage shown on Channel 4 News appears to show an officer striking him with a baton.
The Independent Police Complaints Commission (IPCC) is trying to identify officers who were at the scene.
The IPCC has ordered a second post mortem examination as part of its investigation.