A man who helped police direct traffic after a fatal accident may hold vital information about the incident, officers said.
Motorcyclist Jonathan Gaye, 34, of Fitzcount Way, Wallingford, died after a crash on the A4130 at Gangsdown Hill, near Nettlebed, on February 7.
The road is an accident blackspot, which has claimed the lives of five people in the past six months.
A white man aged about 50 with thin greying hair, who was wearing a jumper and had a local accent, helped close the road after the accident.
Police believe he may hold vital clues to what happened.
Acting Sgt David Hannan said: "We have been told that he was providing good local knowledge concerning other ways to get to Wallingford."
Anyone with information should contact the incident room on 01189 231827, or Crimestoppers anonymously on 0800 555111.
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