Police believe a pick-up driver could have vital information about a crash last month which killed a cyclist.
The collision, which involved a black Nissan Qashqai and a cyclist, happened on the B4009, Tring Hill, Aston Clinton, near to the junction of Upper Icknield Way, at about 10.30am on Saturday 30 May.
The 54-year-old woman cyclist died at the scene.
The driver of the Nissan was uninjured.
Police say they would specifically like to locate the driver of a grey pick-up vehicle, similar to a Nissan or a Toyota, who may have witnessed the incident.
Investigating officer, PC Kelly Hobson of the Serious Collision Investigation Unit based at Bicester, said: “I would like to re-appeal to anyone who may have any information about this collision to come forward and speak to police by calling 101.
“I would particularly like to locate the driver of a grey pick-up vehicle, similar to a Nissan or a Toyota, who may have witnessed the incident. The driver of this vehicle might have vital information that can assist our investigation.
“If you don’t want to speak directly to the police you can contact the independent charity Crimestoppers anonymously on 0800 555 111. No personal details are taken, information is not traced or recorded and you will not go to court.”