Gardaí were last night investigating a drugs link to the shooting dead of a father of one, Eoin Cahill (25), at a party in a house on the Waterford-Tipperary border on Sunday night.
A second man was wounded when two men, both masked and armed, burst into the house three miles from Clonmel, Co Tipperary.
Gardaí arrested three men and a woman on the main Clonmel to Carrick-on-Suir road at about 2am yesterday and brought them to Clonmel for questioning.
They later held another two men for questioning about a break-in at Mr Cahill's house in Cahir.
All six, who are in their 20s and early 30s, were last night still being questioned at Clonmel, Cahir and Tipperary town Garda stations about the killing of Mr Cahill and the wounding of Mark Doolan (36).
Garda sources said it was suspected that Mr Cahill's death was related to an ongoing feud in Clonmel between a number of rival drugs gangs in the town.
Mr Cahill, from Clonmel, was killed instantly when the two raiders, wearing balaclavas and each armed with a shotgun, burst into the house at Poulboy, Kilganey, Co Waterford, at about 11.50pm.
One of the gunmen discharged his weapon, hitting Mr Cahill in the forehead.
Mr Doolan, also from Clonmel, began grappling with the first gunman and was wounded in the arm and upper torso when the weapon went off.
Up to 15 people were in the house at the time. It is understood a number of them began struggling with the gunmen and managed to partially lift one man's balaclava before the two men ran out the front door to a waiting car.
Garda sources said one of the gunmen dropped his weapon in the house. Gardaí yesterday carried out an extensive search of the fields surrounding the dormer bungalow as well as stretches of the nearby River Suir for the second weapon.
Gardaí believe the two raiders had an accomplice waiting in the getaway car and fled in the direction of Carrick-on-Suir, where it is believed they abandoned the car and called to a female friend who then drove them back to Clonmel.
Meanwhile, those at the party raised the alarm and the emergency services were called.
Mr Cahill was pronounced dead at the scene while Mr Doolan was taken in an ambulance to St Joseph's Hospital in Clonmel. He was later transferred to Our Lady's Hospital in Cashel, and from there to Waterford Regional Hospital in Ardkeen, where his condition was last night described as comfortable.
Gardaí have cordoned off the scene and technical experts yesterday carried out a forensic examination. They removed a shotgun, which they believed was used in the killing, for forensic and ballistics examination.
State Pathologist Dr Marie Cassidy carried out a preliminary examination of Mr Cahill's body before it was removed to Waterford for a postmortem. It showed Mr Cahill died from a single gunshot wound.
Mr Cahill had been living at Rosemount Green, Cahir, with his partner, Sharon Rossiter, a sister of 14- year-old Brian Rossiter who died after falling unconscious in Garda custody in 2002, and their two-year-old son, Brian.