The Fishers were found shot and beaten at their home

Graham and Carol Fisher, aged 60 and 53, were shot and badly beaten at their home at the Perch Garage on the A39 near Wadebridge.

Their bodies were discovered on 6 November. It is thought they may have died during Bonfire Night.

Officers say they have a witness who may have seen the vehicle on 5 November. It was stationary in a lane close to where two gun stocks were dumped in a hedge.

Ballistics examination

The stocks, which were from shotguns which belonged to the Fishers, have now been examined by ballistics experts and police say they were not used in the murders.

However, police say it is vital the car is traced.

Police spokesman Pc Baxter Provan said: "The witness saw a stationary vehicle. The headlights were on, so she couldn't get a good look at it.

"But it was close to where the gun stocks were found, and it left at high speed towards the A39, the main road.

"We're very keen to trace this vehicle to eliminate it from our inquiries, otherwise it's going to be considered that it was possibly used by the offenders."