Ten people held in connection with the fatal shooting of Seán Winters in Portmarnock, north Dublin, on Sunday evening have been released without charge.
The seven men and three women, aged between 24 and 56, were arrested at a number of locations across north county Dublin shortly after the shooting occurred.
Files are to be prepared for the Director of Public Prosecutions (DPP).
Mr Winters (42), originally from Raheny, north Dublin, was shot dead outside the gated apartment block where he lived in Portmarnock in the north of the city.
He was shot on Station Road near the entrance to the Links apartment complex at about 10.30pm.
Locals reported hearing a scuffle – or running – outside the building before the gunfire that killed Winters.
A postmortem later revealed Winters had been shot twice in the head with a 9mm handgun.
The car used in the killing – a 98 OY silver VW Passat – was found on fire at Templeview Close, Coolock, just after the murder.
Gardaí believe Winters was involved in a large drug-dealing gang operating mainly in Donaghmede and Baldoyle, both in north Dublin. A leading member, David Lyndsay (38), and his friend, Alan Napper (39), went missing in 2008 and are presumed murdered.
Another member of the gang, Paul "Burger" Walsh (29), Foxhill Green, Baldoyle, had €600,000 confiscated by the Criminal Assets Bureau three years ago.
Winters was the chief suspect in the murder of Anthony Jenkinson (28), who was beaten to death in St Anne's Park, Raheny, in April 2001. He was killed in a dispute over drug money. Winters was a cousin of Noel Deans (27) who was shot dead in Coolock in January.
Gardaí are trying to establish whether he was planning revenge against those who had murdered his cousin, and may have been killed to prevent such an attack.