A man, 27, has been arrested in connection with the Jim Attfield murder investigation.
The arrest, the third since Mr Attfield was discovered with 102 stab wounds near Castle Park early on March 29, comes as Essex Police make fresh appeals for witnesses.
It has emerged only two of the 23 captured on CCTV walking past Lower Castle Park late on March 28 and in the early hours of Saturday March have been identified.
In particular, they want to speak to the three men pictured in these two CCTV images.
Police today carried out raids on two further properties in Colchester.
Detective Chief Inspector Simon Werrett said: "Two of the people featured in the CCTV images we have released have come forward and have been spoken to and eliminated from our enquiries.
"That still leaves 21 people who we need to speak with and who may hold important information in relation to our investigation.
"In particular we are keen to gather further information about the group of three people in images 5 and 5a. I would like to hear from anyone who saw this trio at any time during the evening but in particular between midnight and 2.15am.”
Anyone with information should call Essex Police on 101 or Crimestoppers anonymously on 0800 555111.
Crimestoppers has offered a £5,000 reward for information leading to the arrest and conviction of the person, or persons, responsible.