Two men arrested yesterday in prison as part of a murder probe are also suspects for the attempted murder of another gangster, who was shot dead last year.
Details of the west Dublin gun murder bid cannot be outlined here for legal reasons and the suspects were last night returned to jail.
The two men from Ballyfermot and Clondalkin were quizzed for hours before being released without charge.
The pair were lifted in relation to the brutal murder of Thomas McCarthy, who was shot dead at his mother's home at Ballyfermot on July 27.
The suspects, aged 32 and 24, were arrested in Dublin this morning but neither is suspected of being the gunman.
Instead they are believed to have helped the brutal killer who is thought to have fled the country shortly after the murder.
Gardaí believe that Mr McCarthy travelled back to the capital from his home in England to "seek retribution" after a 25-year-old local criminal brutally assaulted a woman who was well known to the victim.
However, it was a case of who could strike first and Mr McCarthy was gunned down in a hail of bullets from a handgun by his killer who wore a mask when he called to the door.
A senior source said that four shots were fired at Mr McCarthy when he answered the door and another four shots were fired at him inside the house as he tried to escape the lone gunman.
Mr McCarthy was married with children and had been living in Essex - he had only been back home for just over a week when he was shot dead.
The chief suspect in the case fled the country in the aftermath of the murder and is under death threat from criminal associates of Mr McCarthy, including from members of the notorious 'Dee Dee' O'Driscoll gang.
His murder is the only gun slaying in the capital this year and the arrests were announced by a garda spokesman yesterday morning.
The gunman escaped in a Ford Fiesta, which was found burnt out nearby.
He then got into a Skoda Octavia and drove to Monksfield Walk in Clondalkin.
This car was also burnt out with the suspect fleeing on foot.
Gardaí believe he then got into a waiting Toyota Avensis, 10-D-123251.
This car was spotted on CCTV between 10.57am and 11.06am at Woodford Lawns, a five minute walk from Monksfield Walk.
The Avensis was found burnt out on Peamount Road, a quiet country road about 15 minutes away in Newcastle, Co Dublin.
The chief suspect in the case is a 25-year-old who had about 20 criminal convictions before he even turned 18.
"Two men were arrested on the morning of Friday, October 16, 2020, in connection with a fatal shooting incident that occurred in Ballyfermot on Monday, July 27, 2020," the garda spokesman said.
"A man (mid-50s) sustained fatal gunshot wounds after opening the front door of his home in Ballyfermot at approximately 11am on Monday, July 27, 2020.
"The two men, aged in their early 30s and mid-20s, were arrested this morning under the provisions of Section 42 of the Criminal Justice Act 1999 and are currently detained under Section 4 of the Criminal Justice Act, 1984, at Lucan and Clondalkin garda stations.
"Gardaí are continuing to appeal to any person with information on this fatal shooting incident to make contact with Ballyfermot garda station on 01 666 7200, the Garda Confidential Line 1800 666 111, or any Garda station," he added.