Officers have until Tuesday to detain the men without charge and quiz them on a series of late-night assaults in the town after three of them were arrested on suspicion of murder when a man - named locally as Darren Lock - was found stabbed to death at his flat in Queen's Road shortly after 10pm.
The men, aged 20, 22 and 32, have also been arrested on suspicion of attempted murder after a 33-year-old man was found with serious injuries in Boundary Road at 9.30pm. He was taken to hospital, where he remains in a stable condition. He has been named by neighbours as Danny Black.
The 20-year-old man will be quizzed on suspicion of assaulting a 43-year-old woman in Howarth Court at about 9.30pm, who was out walking her dog and suffered serious injuries to her leg, and all three men will be questioned about an assault on a 43-year-old man near The Plough pub in Greenham Road at about 10.30pm, who sustained bruising.
The 20-year-old and 22-year-old have also been arrested on suspicion of assaulting two men, aged 21 and 22, in Thatcham town centre at 1am on Saturday.
A fourth man, also aged 32, has been arrested on suspicion of assisting an offender.
Formal identification of the victim is expected tomorrow and senior investigating officer, Detective Chief Inspector Joe Kidman said: "Our investigation is progressing and we will be continuing our enquiries in the areas concerned in the coming days.
"We are still very keen to hear from any witnesses to these events in the Newbury and Thatcham areas on Friday evening and Saturday morning, or from anyone who has other information that could assist our investigation.
"Neighbourhood officers have been carrying out additional patrols to help reassure local residents. Anyone with any concerns is asked to speak to those officers or call the Police Enquiry Centre on 101."