Gunmen fired up to 15 shots from automatic handguns as they shot two young cousins at a Tesco petrol station in the Republic of Ireland.
The victims, Glen Murphy (19) and Mark Noonan (23), had no known links to gangland crime and gardai have not yet established a motive for the bloody double murder.
They were met with a hail of bullets after stopping off on their way from a girlfriend's house to buy cigarettes.
The three-man killer gang was already waiting in the forecourt of the Tesco petrol station beside the Clearwater Shopping Centre in Finglas, Co Dublin.
Last night, Glen Murphy's mother Geraldine told how her son had texted his usual "goodnight" message to her, just 10 minutes before he was brutally murdered.
Detectives were last night trying to determine whether the gunmen had advance knowledge of their victims' planned stopover at the garage, as they appeared to be waiting for their arrival.
The victims had driven their grey Toyota Avensis car along Rathborne Drive and on to the River Road before pulling into the station, around midnight on Tuesday.
Mr Noonan, from Drumalee estate, off the North Circular Road, parked the Avensis near the hatch at the garage shop and walked over to buy the cigarettes.
The gunmen pulled up close by in their dark-coloured BMW 5-series car and one of the passengers immediately began firing with his pistol from the back seat.
In the meantime, Mr Murphy, from O'Devaney Gardens in the north inner city had stepped out of the Avensis while waiting for his friend.
As the bullets flew, he tried to run, but was caught between one gunman and the BMW, which had moved in front of the Avensis.
He jumped back into the Avensis in an attempt to hide, but was shot several times in the stomach and head as he tried tried to clamber to safety.
A number of bullets struck Mr Noonan in the back of his head and in his back as he stood at the hatch.
The gunmen and their accomplice, who was driving the BMW, then sped off, possibly along Finglas Road.
Last night, members of the 60-strong garda investigation team were sifting through CCTV footage from the area, as they believed this could contain vital clues to the identity of the killers.
Gardai said the killers had been driving the BMW around the forecourt for several minutes before ambushing their victims.
Detectives have already interviewed a number of late-night shoppers and motorists who were in the area at the time and have appealed to others, who might have spotted either the Avensis (reg no 05 D 86211) or the BMW with a 06 D registration plate to contact the incident room at Finglas garda station, on 01 6667532, or the confidential line, 1800 666111.
Officers from the national bureau of criminal investigation joined gardai from Finglas and the Bridewell for a case conference yesterday.
One detective said : "It looks like the two victims fell foul of a major crime gang, but at this stage of the investigation we don't know yet know why.
"There is nothing to suggest they might have been involved in serious crime, but we are examining all options".
It emerged yesterday that some of the garage staff and customers were lucky to avoid the gunfire.
Supt John Gilligan said one member of staff had been standing behind the glass hatch when the gunmen pulled alongside, while a customer had walked away from the hatch seconds earlier.