Glennon, 30, died of multiple gunshot wounds as he tried to flee a gang of four who had lain in wait for him close to the neighbourhood where his home is located in the early hours of Saturday morning.
But gardaí believe the killers risked appearing conspicuous by hanging around the area in a large group because they intended abducting him and possibly torturing him before disposing of his body.
It is not clear what caused the gang to change their plans and shoot their victim at the scene but it is likely they realised they had been spotted by a number of people, including an off-duty garda who called for back-up.
Despite being hit several times in the upper body, Glennon managed to start his car and drive a few hundred yards before collapsing at the wheel.
The Meath-registered Mazda came to a stop after mounting a footpath.
Glennon was attended to by an ambulance crew but he died about an hour later in hospital.
Detectives hunting the killers are targeting known criminals amid fears that Glennon’s death could lead to a round of tit-for-tat murders.
While the dead man’s official criminal record was not extensive, he was known to gardaí as a key member of a drugs gang operating out of the Blanchardstown area in northwest Dublin which was formerly controlled by the notorious Westies.
It was the fourth gangland killing in Dublin in a month and although the incidents do not appear to be related, opposition politicians claimed they were alarming evidence that the war on gun gangs was being lost.
Labour justice spokesman Joe Costello accused Justice Minister Michael
McDowell of being “totally preoccupied with his personal battle” with the Prison Officers’ Association with whom he is in a bitter and protracted dispute over overtime pay.
“The struggle against the criminal gangs appears to have been allowed to slip way down the ministerial agenda.”
Earlier this year Minster McDowell declared a legislative crackdown on gun crime, announcing his intention to introduce mandatory sentences for weapons offences under the new Criminal Justice Bill currently before the Dail.
Gardaí, meanwhile, yesterday continued their examination of the murder scene on the Dublin-Meath border where Andrew Glennon, who lived at Fortlawn Drive, Blanchardstown, was shot at about 4am on Saturday morning.
The murder weapon has not been found and may have been dumped in the nearby Royal Canal. Several witnesses heard the commotion and saw the gang run from the scene but the men were masked and no clear descriptions have emerged.
An incident room has been set up at Blanchardstown Garda Station.
Anyone with information is asked to contact on 01-6667032.