John Daly, the Dublin criminal whose call to RTÉ Radio's Liveline provoked a clampdown on mobile phones in prisons, was shot dead overnight in Finglas.
The 27-year-old was shot a number of times while sitting in a taxi with friends following a night out at around 1.45am on Cloonlara Drive.
He was later removed to the Mater Hospital where he was pronounced dead.
Daly had been warned that his life was in danger and was given advice on his personal security.
Gardaí say the driver of the taxi who was sitting beside Mr Daly is lucky to be alive.
Daly slumped over the 40-year-old taxi driver as he was shot at least five times during the attack in Finglas.
The taxi driver's family say the killing has left him traumatised and terrified.
The scene of the shooting has been preserved for technical examination and the State Pathologist has been notified.
Supt John Hartnett confirmed that gardaí had recovered a burned out dark-coloured jeep in nearby Scribblestown Park which they believe was the getaway vehicle.
In the aftermath of this morning's shooting, Taoiseach Bertie Ahern said it was time society stopped tolerating casual violence on the streets.
The Labour Party's Justice Spokesman, Pat Rabbitte, has said there is now a need to put the witness protection programme on a statutory basis.
Mr Rabbitte said Ireland is experiencing an escalation of crime, which highlights the need for crime bosses to be targeted.
He said Mr Ahern's comments portrayed him as some kind of 'bewildered bystander' rather than the Taoiseach of the country.
An incident room has been set up at Finglas Garda Station and gardaí are appealing for witnesses to contact them at 01 666 7512.
