Two men arrested on suspicion of the murder of a man from Annan have been released on bail.
Paul Taylor, 56, from Annan, Dumfries and Galloway, was last seen as he travelled to Carlisle on 17 October.
Police Scotland had said officers were concerned for his welfare.
But on Wednesday Cumbria Police confirmed its inquiry had been upgraded to a murder probe and two 19-year-old men from the Carlisle area were arrested.
The force earlier said a 37-year-old man, from Carlisle, and a 17-year-old boy, from Appleby, were also in custody after being arrested on suspicion of assisting an offender.
Detectives are keen to hear from anyone with information about the Mr Taylor's movements or those of his car - a blue Vauxhall Corsa, registration PY18 DYO - between the night of 17 October and the morning of 19 October.
He had left his home at 21:45 and travelled along the M6, southbound.
Police believe the car then headed in the direction of the Kingmoor South area of Carlisle, at about 23:35, and was in the Carlisle West area.
They are keen to hear about sightings of the car, specifically in the Yewdale, Sandsfield Park and Burgh Road areas.
The car was found abandoned in Langwathby at about 08:45 on 19 October.
Anyone with information should contact Cumbria Police.