Police have appealed for two people who have been seen on CCTV to come forward to help with a murder investigation.
Essex police Detective Chief Inspector Simon Werrett, investigating the stabbing of James Attfield, said officers are keen to trace a woman who was seen in an image on March 29 at 12.36am and again with a man on another image at 2.19am.
Detectives are trying to piece together Mr Attfield's movements between the evening of March 28 and when he was found the following morning just before 6am with more than 100 stab wounds in Lower Castle Park, Colchester.
He had died at the scene a short time after he was discovered.
Mr Werrett said: "I would urge these two people to come forward or if anyone recognises them I would ask them to get in touch with the enquiry team."
A police spokesman said the man is described as white, of stocky build and appears tall with long legs. The only description of the woman is that she is white. They were sitting at opposite ends of the bench and it is not certain if they know each other, although they may have been a couple who had a row earlier in the evening and were sitting apart not talking to each other.
Approximately 10 metres away from where this couple sat, there was a man sitting on the grass who was white, aged in his 30s and wearing a dark jacket and possibly jeans. This may, or may not, have been James Attfield, the spokesman said.
Police have now ruled out three people who were also spotted in the area on CCTV.
The three people came forward voluntarily to spoke to Essex Police after they were pointed out on CCTV. They have been eliminated from enquiries, the force said.
A total of six people caught on CCTV walking through Lower Castle Park have now been identified and eliminated from enquiries. A further 17 people have yet to come forward.
A man and a woman, both aged 27 and from Colchester, have been bailed until May 9 pending further enquiries.