In the past month, five people have died in unlinked gangland feuding. Gilligan was shot 48 hours after Sligo man Hughie McGinley, 26, was gunned down in a van in Sligo. His death is associated with feuding between two local families.
Gilligan, 30, originally from Fortlawn Drive, Clonsilla, had been living with his partner and children at Huntstown Wood, a housing estate near Clonee village on the Dublin/Meath border.
He was shot several times at close range early on Saturday morning after four men ambushed him in a Clonee housing estate.
Detectives are working on the theory he was lured to his death after agreeing to a pre-arranged meeting at Bramblefield Court, adjoining Huntstown Wood.
The victim had left his car at the junction of Bramblefield Drive and Bramblefield Court, Clonee, at about 4.15am when he was attacked, but managed to retreat under automatic weapons fire and drive off before the car came to a halt on a footpath. He then tried to run away but collapsed on Littlepace Road.
The gang escaped on foot. An off-duty garda phoned for assistance and the victim was taken to James Connolly Memorial Hospital, Blanchardstown, where he died a short time later.
Gilligan was a member of the Westies gang in Blanchardstown in the late 1990s but fell out with leaders Shane Coates and Stephen Sugg. Both went missing in Alicante, Spain, in February 2004 and are feared dead. It is believed Glennon was part of the gang that killed Bernard Sugg, 23, a brother of Stephen Sugg, in a Dublin pub in 2003.
Meanwhile, gardaí believe they are close to charging the key figures behind the abduction of the Richardson family and the subsequent robbery of 2.4 million from a Securicor van. Last week, 24 people were arrested and questioned in a major garda swoop, but released. DNA samples taken from seven criminals are being cross-checked against samples gathered from locations and items used during the abduction and robbery on March 13 and 14.