The four, all aged in their 20s, were arrested in a coordinated swoop by gardaí at 8am.
Maurice Martin, 21, died after being repeatedly stabbed in the neck and chest in the early hours of 12 June.
His body was found on open ground near a busy junction in Finglas, north Dublin, at around 5am by a passing taxi driver.
He had suffered significant blood loss over a large area, suggesting he was trying to get away from his attacker and seek assistance.
He died a short distance from Kippure Park, where he was originally from, before living in a number of areas, most recently Navan, Co Meath.
Mr Martin had been drinking overnight at a party in a nearby house.
Gardaí yesterday said they arrested one man, aged 24, and three women: aged 20, 21 and 22.
They were picked up at various locations in the Finglas area at 8am.
They were all being questioned under Section 4 of the Criminal Justice Act in connection with the murder. They were held in separate stations, including Finglas, Blanchardstown and Cabra.
Gardaí have focused much of their investigation since Mr Martin’s murder on who he was in contact with during the course of the night.
Mr Martin was one of two Finglas men murdered on 12 June. The second Paul Smyth, aged 34, was found shot dead at Balbriggan, north Dublin.
His murder is believed to be part of a gangland feud in the Finglas area.
His murder was followed five days later by the shooting dead of Tommy Joyce in Darndale, north Dublin.
The 20-year-old Traveller was a significant player in a major drug trafficking gang, which operated out of Grove Lane halting site, where he lived with his family.
Both the Smyth and Joyce murders are due to be featured tonight on Crimecall on RTÉ. Investigating officers will appeal for information in relation to both deaths.
Joyce’s murder was the 15th gangland gun killing so far this year.