Robert Rose, 59, said he saw a light-coloured Ford Fiesta being driven at a farm owned by Hector Dick, the man incriminated by Nat Fraser over the death of his wife.
Mr Rose said he was sure Mr Dick had not been the driver, but he could not rule out the possibility it was Fraser.
The High Court in Edinburgh has been told in evidence by Mr Dick that he acquired a beige Ford Fiesta for Fraser shortly before Mrs Fraser, 33, vanished from her home in New Elgin, Moray, in April 1998.
He said the car was returned to his farm at Mosstowie, near Elgin, a few days later.
He got up one morning to find it there, and he suspected it had been involved in Mrs Fraser’s disappearance. He stated that he burned and crushed the vehicle, and took the wreckage to a scrapyard.
Mr Rose told the jury he worked as a painter and decorator in 1998, and had a job at Mr Dick’s farmhouse. He could not be precise about the date, but thought it was about the time of Mrs Fraser’s disappearance.
It was several months later that he learned the police were interested in any information about a beige Ford Fiesta, and he came forward and gave a statement.
“I was working in an upstairs bedroom and looking out the window and I thought I saw a car similar to the one they were looking for ... a light-coloured Ford Fiesta,” said Mr Rose.
The car was driven to the entrance to a field. There was one person in it, a man.
“It was not Hector Dick. I know him,” said Mr Rose.
Another vehicle, a green lorry, appeared and its driver opened the gate to the field and both the car and the lorry drove in and along a track, out of his view.
Mr Rose added that he had contacted the police because he thought the car he had seen might have been the car in the appeal for information.
“I could not be sure ... it was just a passing glimpse,” he said.
Mr Rose had not known Fraser, but had seen him, some months after the incident at the farm, on television making an appeal for information about his wife’s whereabouts.
Asked if either of the drivers he had seen was Mr Dick, he said: “No.” But it was possible, he continued, that one had been Fraser.
“I did not take a good look at the people. I was not staring at them or anything,” he said.
The defence solicitor-advocate, John Scott, QC, put it to Mr Rose: “You are not saying it was Nat Fraser.”
Mr Rose said: “No. The only thing I know for sure is it was not Hector or Jimmy (Mr Dick’s brother).”
The advocate-depute, Alex Prentice, QC, asked: “Is there anything that would absolutely exclude Nat Fraser as being one of these persons?”
Mr Rose said: “No.”
The court has heard that Fraser had an alibi for the day his wife went missing. He was making deliveries for his wholesale fruit and vegetable business.
Ronald McDonald, 71, a retired butcher, said he was one of Fraser’s customers.
“He was always light-hearted, joked with the staff, very sociable,” said Mr McDonald.
“(That day) I saw nothing different. As far as I can recollect, just his usual banter,” he added.
Fraser, 53, denies acting with others to murder his wife. He pleads alibi and incrimination, blaming Mr Dick and another or others if she was killed.
The trial continues.