Gardai are expected to investigate "a long list of suspects" in the murder of Mark Desmond, the gangster known as the 'Guinea Pig'.
The notorious hood (41) was shot up to four times in the head in Griffeen Valley Park, Lucan, at around 8pm last night.
Senior sources last night said there would be a "long list of suspects" in the murder, as Guinea Pig had made a number of enemies throughout his lengthy criminal career.
Gardai are already investigating Desmond's link to two criminal brothers based in the locality.
Desmond was implicated in at least four murders, including the infamous 'canal murders' investigation in 2000.
Patrick Murray and Darren Carey were shot in drug-related killings and their bodies dumped in the Grand Canal at Karneystown, Co Kildare, between December 19, 1999, and January 10, 2000.
Desmond was arrested but the charges were later dropped.
Gardai will examine if this could have acted as motivation for his killing last night, despite the two-decade gap between the crimes. However, it is understood that this will be examined along with a number of other emerging theories as the investigation progresses. Gardai are also probing whether Desmond was in the area to meet a local drug dealer before he was gunned down. The career criminal was known to associate with criminals from the Lucan area, among other criminals from Co Dublin, Co Wicklow and Co Sligo.
It is understood that a gunman approached Desmond on the Griffin Glen Park road, before chasing him into the adjacent park and shooting him up to four times in the head.
Another previous crime which may be linked to his murder is the killing of James Kenny McDonagh (28).
Mr Kenny McDonagh who disappeared in October 2010, was shot in the back of the head and his body buried in a shallow grave. A major line of enquiry is whether Mr Kenny McDonagh was targeted in retaliation for an attack on Mark 'Guinea Pig' Desmond in the Memorial Park in Ballyfermot in April, 2010.
On that occasion, Desmond managed to escape from his attackers on a quad bike when they approached him in the park. His body remained in the park last night, near a skate park and football pitches which are used by dozens of youths and adults on a Saturday.
Dublin Fire Brigade (DFB) responded to reports of a burned out car on nearby Hayden's Lane shortly after the shooting. It is believed that this vehicle was used as the getaway car in the gangland shooting.
All entrances to Griffeen Park remained sealed off last night as detectives carried out door-to-door inquiries.
Garda forensic officers also attended the scene shortly after 9.30pm to carry out a preliminary technical examination of the scene. Detectives also stopped and searched a BMW car which was acting suspiciously near the scene.
Armed gardai blocked the car in at a cul de sac, before searching the vehicle and the occupant. However, after being briefly questioned he was told to the leave area. Locals in the Lucan estate expressed shock at the shooting in what they described as a very quiet area.
"I heard the helicopter overhead but didn't think too much of it, until around half an hour later when more Garda cars started arriving on the road," said one man, who lives beside the park where Desmond was shot dead.
Another local man said: "People always think this couldn't happen in there area, that their exclusive. They're not, it can happen anywhere.
"I walk in that park all the time, even at night with my kids. Unfortunately it'll always be known as the park where Mark Desmond was killed".
Meanwhile, Tanaiste Frances Fitzgerald has condemned the "brutal attack" which she said is another reminder of the "callous disregard for human life displayed by people intent on murder and mayhem."
"An Garda Siochana will continue to take every possible measure to counteract activity of this kind and will have the continued support of the Government and the community in doing so," Ms Fitzgerald said.
"Every effort will be made to bring the perpetrators of this dreadful shooting to justice and we will face down those who mistakenly think they can get away with these evil acts."