Michael Pritchard, 54, of Blurton in Stoke-On-Trent, was killed when his own van was driven into him in the Kirk Langley area of Derbyshire on November 12, 1997.
At the time the police investigation led officers to enquiries in the Bradford and Derby areas but the killer has never been caught and brought to justice.
Those lines of enquiry are being reopened, the Derbyshire Constabulary said, as the case was relaunched two decades after Mr Pritchard’s death.
Detective Inspector Toby Fawcett-Greaves who is leading the re-investigation said: “We have previously followed lines of enquiry in the Bradford area which we are re-visiting. We believe there may be people in the Derby and Bradford areas who hold relevant information in relation to this investigation and I would urge them to contact us.”
It was 3.20pm on a Wednesday when Mr Pritchard was delivering a parcel to a house on The Cunnery in Kirk Langley and he became aware of his own van manoeuvring behind him.
In an attempt to stop his van being stolen, Mr Pritchard stood in front of the vehicle but it did not deter the thief who drove away at speed, running Mr Pritchard over and dragging him a considerable distance along the road.
Mr Pritchard died instantly from his injuries.
The driver appeared to be with two other men, who were in what is believed to be an E-registered Bedford Rascal van.
Mr Pritchard’s van, a white Sherpa 200 with a ‘Business Express’ livery, was driven away onto the A52 and then Brun Lane where it was abandoned.
The Bedford Rascal van took the same route to Brun Lane, where it collected the murderer and drove off.
Det Insp Fawcett-Greaves said: “This case has never been closed; as and when information has been received enquiries have been made.
“Although we are 20 years on we would like to get justice for Mr Pritchard’s family who have had to live all of this time with not knowing who murdered their husband and father.
“We would particularly like to speak to the driver and passenger of the Bedford Rascal van. We recognise the difference in their involvement in the crime to that of the murderer, but we believe they have the crucial information we are looking for to enable us to bring the murderer to justice.
“We are confident that the murderer and the drivers of the Bedford Rascal have spoken to people after the event. These people may have vital information that could assist us in our investigation.”
The driver of Mr Pritchard’s Sherpa van was described as white, 19 to 20-years-old and 5ft 9ins. He was of a medium build with a round oval face and fair, collar-length hair which was thicker at the back.
The driver of the Rascal van was also white and around the same age with fair/ginger, collar-length hair. He had a gap in his upper left teeth.
The passenger was white, aged in his late teens and had short, light brown hair.
Making a fresh appeal for information, Insp Det Fawcett-Greaves added: “Did the people involved tell you anything following the incident? Were you friends with them or in a relationship with them at the time? If so please contact our investigation team.
“Forensics have improved a lot over the last 20 years and we will be re-examining material that was originally submitted.”
Anyone with any information in relation to the investigation, is asked to call Derbyshire Police on 101, quoting incident number 409 of November 9, 2017 or Crimestoppers on 0800 555 111.