Daniel Gaynor should have been in prison when he was gunned down in front of his children.
Gaynor (24) would have been in jail for breaching the terms of a suspended sentence had he not appealed the decision immediately.
Detectives are investigating whether the motive for Gaynor's murder was his suspected involvement in the shooting dead of an associate of Eamon 'the Don' Dunne.
The father of two was the alleged gunman in the killing last month of Colm 'Collie' Owens, who was part of Dunne's gang.
He was also believed to have carried out a shooting on behalf of a former IRA member which left innocent postman Robert Delany in a permanent vegetative state.
Gaynor, from Berryfield Drive, Finglas, was the 18th person to die in gun attacks so far this year.
Members of the Finglas gang once led by Dunne are now the main suspects for the hit.
As well as the murder of Owens, Gaynor was wrongly believed by gangsters to have been the hitman in the killing of the Don himself.
Gaynor was given a three-month sentence in March for repeatedly punching another man who he had blamed for attacking his brother.
However, Judge David McHugh suspended the sentence for a year.
The custodial sentence was then activated last month when Gaynor was brought before the court again for public order offences.
But the criminal immediately appealed the decision and was able to walk free.
Gaynor also had other charges pending. They related to threatening and abusive behaviour and failing to follow the directions of a garda at Barnamore Grove on May 7, 2010.
Blanchardstown District Court heard he had told gardai: "Look at you all. You think you're hard in your uniform and with all your back-up. Take off your uniform and let's see how hard you are."
Gaynor was the chief suspect for the shooting dead of Owens (34), of Dunsoughly, Finglas.
Owens was murdered when a masked gunman entered the Corn Store, an animal feed warehouse, on the Grove industrial estate at Dubber Lane, Finglas, and targeted him.
It is believed Gaynor was hired as a contract killer to carry out the murder on behalf of other criminals.
Gaynor himself was just seven years old when his own father, Robert McGrath, was shot dead by gardai.
McGrath was killed after he pointed a sawn-off shotgun at officers during the course of a foiled armed post office raid by his criminal gang in Co Meath in 1992.
Gaynor followed his father into a life of crime.
At the age of 19 he was jailed for six years for firing a gun through the window of a house because a teenager living there owed him €100.
Just a year later, Gaynor was handed a further two years in jail for intimidating the 62-year-old woman whose home was attacked in the shooting.
In that trial, the court heard how Gaynor approached the woman while she was waiting at a bus stop and told her that her son's days were numbered.
He then made a gesture to her with his fingers in the shape of a gun and as he moved away shouted that her son was "f***ing dead".
The woman had to be placed in a witness-protection programme and the family was forced to move house.
Gaynor was also questioned about the stabbing to death of Maurice Martin (21) in Finglas in June 2009.