Lincolnshire Police are appealing for the driver of a dark coloured vehicle who witnessed a fatal crash on the A52 at Chapel St Leonards to come forward.
A man in his 20s was killed at the scene of the crash on Hogsthorpe Road at 8am on Wednesday, November 29.
The crash involved a blue BMW car and white Vauxhall Vivaro.
The van driver was taken to Boston Pilgrim Hospital with minor injuries.
A police spokesperson said: “We have spoken to most of the witnesses but would very much like to speak to the driver of a dark coloured vehicle which was travelling behind the BMW towards Skegness.
“We know the driver of this vehicle is not involved in anyway in the collision but will have witnessed it and will have information that will help our investigation.
Sergeant Dave Mitchell, from the Serious Collision Investigation Team, added: “I am directly appealing for the driver travelling behind the BMW car to give me a call.
“There are many reasons why they may not have got in touch already, but please ring and speak to us.”