Paul Williams: Breen once epitomised the new breed of young gang boss.
He once epitomised the new breed of young gang boss to emerge with the new Millennium - a brash, dangerous, drug-dealing murderer for whom there were no behavioural boundaries.
Karl Breen relished the glamorous-sounding sobriquet, the 'Champagne Killer', which he earned after stabbing his best friend to death in a drunken, cocaine-fuelled frenzy.
From the prison cell he called home for seven years, Breen posted pictures of himself on Bebo and YouTube, displaying his bare chest covered with tattoos.
This was the same cell from where he organised drug rackets, shootings, bombings and killings on the outside.
Last October, when he was released from prison, gardaí and Breen's rivals went on the alert for a likely outbreak of violence believing that he was either going to kill or be killed.
But the drug dealer found himself isolated and forced to lie low. Associates said he had become paranoid that his life was in danger.
Karl Breen in 2007 Karl Breen in 2007 In the end it was 34-year-old Breen who apparently precipitated his own ignominious demise with the help of either a drug overdose or a drug-induced heart attack. The once-feared gangster was found by family members in the Finglas apartment where he had barricaded himself from his real - and imagined - enemies.
He was sitting on a foot stool with his back leaning against an armchair.
The Clondalkin and Ronanstown estates were terrorised by shootings and bombings orchestrated by Breen from his prison cell and carried out by his loyal henchmen.
He won't be mourned by the family of Martin McLoughlin, the best pal he killed in a haze of Champagne and cocaine on New Year's morning 2006.
The witnesses to that slaying who were forced to flee the country because they testified at Breen's trial - while their families were terrorised at home for years - can now return to west Dublin without looking over their shoulders.
Gardaí classified Breen, who was originally from Nangor Green in Clondalkin, as an "extremely violent and dangerous" criminal.
Over a two-year period from 2008 to 2010, he unleashed a violent rampage on the estates of west Dublin, targeting gangland enemies and people who owed him drug money.
The campaign was co-ordinated by his most loyal lieutenant, Pierce Reid, who led a gang of over 30 thugs to ensure that Breen retained control of the drug trade by shooting potential opponents. Reid had four bullets tattooed on his torso to mark the number of gangland killings he had been involved in. He was shot dead in 2009.
Gardaí compiled a list of at least 100 incidents in which houses were shot at or damaged by pipe bombs.
In one incident, the mother of the gang's intended victim was shot and seriously injured. In others, young children were lucky to escape unhurt.
On another occasion, cars belonging to two prison officers were set alight as Breen expressed his dissatisfaction at being moved from Mountjoy to the Midlands Prison.
The home address of a local detective who had crossed his gang was daubed on a wall in the area to show they knew where he lived.
In a demonstration of his defiance, Breen set up his own Bebo/YouTube pages, which displayed pictures of him posing in his cell.
In one picture, Breen posed with a photograph of a former friend in his hand: it was a message that the guy had crossed the line and was now a marked man.
He even posted a demonstration video for a Glock automatic handgun - the preferred weapon of choice for most gangs, including Breen's.
