A CCTV image of a potential witness has been released as detectives continue to investigate the murder of Jim Attfield.
The man was walking through the park in the early hours of Saturday, March 29, the night Mr Attfield, 33, of East Bay, Colchester, was killed.
He was stabbed 102 times near Castle Park and Guildford Road and died shortly before 6am.
He was last seen in the River Lodge Public House on Middleborough on Friday, March 28.
He left there shortly after 10pm, and police have not had any confirmed sightings of him thereafter until he was found the following morning.
Det Chief Insp Simon Werrett said: "This man looks to be talking on his mobile phone and is wearing a waist length jacket.
"We are keen to speak to him so we can dismiss him from the enquiry."
Anyone with information is asked to call Essex Police on 101 or Crimestoppers anonymously on 0800 555 111.
A man and a woman, both aged 27 and from Colchester, are currently on police bail until Wednesday, July 9, having been arrested in connection with the murder.