Detectives investigating the death of a vulnerable 33-year-old who was found with more than 100 stab wounds have renewed an appeal for help from the public.
James Attfield, of East Bay, Colchester, died last Saturday after he was found with serious injuries in Lower Castle Park just before 5.45am.
A 38-year-old man, from Colchester, was arrested but later released without charge.
Police were at the scene of the attack from about 9pm last night until dawn this morning talking to people who may have been in the park at the same time last Friday.
Officers said they wanted to trace a man and a woman who would have been sitting on a bench in the park at about 11.30pm last Friday night.
Detector Chief Inspector Simon Werrett, who is leading the murder investigation, said today that extensive investigations were continuing in a bid to find the killer.
DCI Werrett said: "We spoke to about 50 people during the course of the night and we have been given some useful information that is currently being followed up.
"We also want to trace a man and a woman who would have been sitting on a bench in the park, by the lake. The only description is they were white and may have been smoking. This would have been about 23.30 on Friday evening.
"We also want to hear from anyone who may know someone who returned home early last Saturday morning with blood-covered clothing which they may have disposed of quickly."
Mr Werrett said that forensic investigations and searches were continuing in the park today and that officers were also searching a council tip for the contents of bins from the park that were emptied at the refuse site during last week.
Mr Attfield suffered a severe brain injury in a road accident four years ago. A post-mortem examination revealed 102 separate wounds on his arms, hands, back, neck and head following last week's attack.