Jamie Bishop said he now feared for his life after his car was set ablaze less than two weeks after it was returned to him by police following the murder of Nattalie Muir.
The 33-year-old was due to give evidence against her killers at their trial and he believes he was targeted in retaliation by their friends or relatives.
Mr Bishop’s upstairs neighbour, Robert Weir, 69, collapsed minutes after the car exploded outside his home in Breich, West Lothian, on Sunday night, and later died at St John’s Hospital in Livingston.
Ms Muir’s father, Calum Muir, was among those who paid respects to the pensioner, adding that he believed no-one who knew his daughter was involved in setting fire to the vehicle.
Police said they were keeping an “open mind” into the motive behind the fire attack in Woodmuir Road.
Ms Muir, 21, was stabbed to death in December last year by a gang led by her schoolboy ex-lover, then 15, who blamed her for aborting their baby.
Mr Bishop was asked by friend and neighbour George Stewart, 34, to drive him, the schoolboy – who cannot be named for legal reasons – and Emma Merrilees, 20, who carried out the fatal stabbing, from Breich to nearby Whitburn on the night of the murder.
He said: “I got a phone call from George Stewart that night asking to go to Whitburn. I was worried he would drive drunk if I didn’t. I’m a bit of a fool and too trusting so I took him, Emma and [the boy], but I had no idea what they were doing.
“They jumped out the car and ran off when I got there. When they came back, Emma showed me the knife and said, ‘Look at the blood on this’. I asked what was going on and George told me, ‘If you say anything, your dad is next’. Then he threw the knife out the car window.
“I was a witness but I never had to give evidence at the trial because they pleaded guilty. That’s why I think someone who knows George or [the boy] or Emma might be involved in what happened to my car.
“I’m worried my life is in danger. The police had already put an alarm in my house. I don’t know what might happen next but I’m worried about my dad. The police have offered to re-house me, but my dad won’t move and I won’t go without him.”
Mr Bishop said he had met Ms Muir a few times, driving her and [the boy] to Edinburgh on one occasion, and also knew Merrilees.
Police returned Mr Bishop’s Peugeot 406 on November 3 after holding it for forensic tests until the trial was completed.
Mr Bishop added: “I was at my dad’s when the firefighters came looking for me on Sunday night. They wanted to check inside my house and needed keys.
“When I went round, the police wouldn’t let me near it. I saw Robert Weir being taken away in an ambulance stretcher. It’s terrible because Mr Weir was a lovely man.”
Mr Bishop’s father, John, 75, said: “My son’s a big softie. These people took advantage of him to get a lift that night and that’s how he became involved in all this.”
In August, the schoolboy, now 16, was jailed for six years while Stewart was jailed for eight years and five months after they admitted the culpable homicide of Ms Muir. Merrilees was handed a life sentence and ordered to serve a minimum of 16 years for murder.
Mr Muir, 42, said: “I read about the man dying in the Evening News. I had no idea it might be connected to Nattalie’s murder. I don’t think anyone Nattalie knew would be involved.
“My sympathies go out to the man and his family.”
James Haggarty, 49, paid tribute to Mr Weir, a retired sheet metal worker, whom he had known for more than 40 years. He added: “He had problems with his blood pressure and it was probably the shock of the fire that killed him.”