Three young men standing around gangster Stephen "Madzer" Byrne moments before he was gunned down scattered when his killer arrived on a bicycle, detectives indicated today.
Their timely exit from the scene has sparked suspicions of involvement in luring the 32-year-old to his violent murder yards from a church in Dublin's north inner city.
Two of the suspects - one a juvenile and the other in his 20s - are being questioned at Store Street garda station.
Gardaí are tracking down the third man who was standing with Byrne before he was shot dead at the corner of Sheriff Street and St Laurence Place East.
Detectives say the lone gunman cycled up to serial criminal Byrne and the others at the junction near the capital's financial district at around 4.40pm yesterday.
The killer was wearing a grey hooded top and a balaclava and is believed to be young because he was "fairly agile".
When he dismounted the black mountain bike, thought to have been stolen and spray-painted, the three others scrambled before he opened fire with a handgun.
Byrne was hit in the head first and then in the chest, and was later pronounced dead at the Mater Hospital. There are no reports of anyone else receiving injuries in the attack.
It is understood Byrne received a phone call earlier in the day telling him to meet an associate close to his nearby home.
The killer took off on his bicycle along Seville Place in the direction of the Five Lamps but turned into a side street before reaching the local landmark.
Investigators are unsure if he turned left or right.
They have appealed for anyone who may have seen the attacker on a bicycle to get in contact with them at an incident room set up at Store Street Garda station.
Chief Superintendent Pat Leahy said there would be increased policing in the north inner city in the coming days as tensions rise over possible reprisals.
Byrne, from Mariner's Port, Sheriff Street, was the prime suspect for the murder of Stephen Ledden, 28, in nearby Upper Oriel Street in 2006.
It was one of five killings in the area in a bloody fall-out among criminal associates after notorious gang boss Christy Griffin was accused of the rape of his partner's daughter.
Byrne was also a known drug dealer and thief.
His brother David died a year ago after being savagely beaten in Mountjoy Prison by an inmate using a sock full of batteries. His corpse was later defaced in a funeral home when someone scrawled "rats" on his forehead.
Two other relatives have been shot dead.