A 31-year-old man and 23-year-old woman are currently being questioned on suspicion of assisting an offender and perverting the course of justice.
Police are questioning two more people in connection with the murder of Peter Crowley in Barton.
The 50-year-old was assaulted near to the shops in Underhill Circus, one evening in April.
He was found dead at a property on Brome Place the following morning.
A 31-year-old man and 23-year-old woman, both from Oxford, were arrested earlier today on suspicion of assisting an offender and perverting the course of justice.
Two teens from the city, a 17-year-old boy and a 16-year-old girl, were arrested on suspicion of murder last month, and released on Police bail.