Police are trying to trace two vehicles seen close to the scene of a car fire where the body of a 23-year-old university graduate was found.
Catherine Wells-Burr, 23, was discovered in her red Ford Focus in a field in Somerset on Wednesday.
Officers say they want to talk to the owner of a dark-colour people carrier and a white van seen in the area.
Police have been granted a further 36 hours to question a 32-year-old woman arrested on suspicion of murder.
The two cars were seen on the A358 between Ilminster and Taunton at about 06:10 BST on Wednesday.
The people carrier braked close to the fire, police said, while the white van was parked close to the field where the burning car was found.
Police said they did not know if Miss Wells-Burr was alive when the car was set on fire.
A post-mortem examination began on Friday to establish how she died.
Police also questioned two men but have since eliminated them from the inquiry.
Det Ch Insp Simon Crisp said anybody who saw people "wearing high visibility jackets" in the area should come forward as it may prove "significant to the investigation".
Officers were still trying to piece together information about Miss Wells-Burr's social life, he said.
'Shocked and saddened'
The business analyst worked at Numatic International in Chard.
Her employers said: "Catherine was a valued employee who worked with us in manufacturing during her university holidays and after graduation as a full time employee.
"She moved to our IS department last year to further her career as business analyst.
"We are all shocked and saddened by this tragedy and our thoughts are with Catherine's family and all those affected."
More than 3,500 people have joined a tribute site for her on Facebook.
On Saturday, a minute's silence is due to be held before a football match played by her hometown team Chard.