A man whose body was found in a park died as a result of a stab wound, police have said.
Sam Mechelewski, 20, from Huntingdon, was found dead in Hinchingbrooke Country Park on 1 February.
A post-mortem examination was carried out the following day and specialist police diving teams have searched a pond nearby for the weapon.
Cambridgeshire Police also released images of a black Audi A3 seen in the area on the evening of 31 January.
A man arrested on suspicion of Mr Mechelewski's murder has been released under investigation.
The Metropolitan Police divers have been searching a pond near woodlands and at the edge of the park.
Officers believe he was killed in a "targeted attack".
His body was found by a member of the public at about 13:00 GMT in a wooded area of the park.
Det Ch Insp Adam Gallop said: "We're appealing for anyone who has seen [the Audi A3] in the Huntingdon area to get in touch as a matter of urgency.
"It may have been parked by the side of the road."
Police arrested two people from the area on suspicion of murdering Mr Mechelewski.
A man in his 20s from Chatteris has been released under investigation.
A man from Brampton, also in his 20s, was released with no further action being taken against him.