Gardai have arrested one suspect and expect to make many more arrests in the coming weeks in relation to the gangland murder of David 'Daithi' Douglas, who was shot dead last July.
Douglas was shot six times in the head and chest outside the entrance to the Shoestown shop on Dublin's Bridgefoot Street at around 4.10pm on July 1 by a lone gunman.
He was targeted as he walked to his wife's shop after attending a family funeral.
Douglas survived an assassination attempt near his Cabra home last November. The suspects for that failed hit are also being investigated for organising the murder.
"This is a massive investigation which has shown up many very significant issues," a source said.
"This may involve the Kinahan cartel, but it also could be about money owed."
Detectives are investigating whether he became a target for the cartel after he was wrongly blamed for being involved in a plot to kill cartel associate Liam Roe outside the Red Cow Hotel on the night of November 6.
However, Douglas was not at the Red Cow as he was involved in a pub brawl in Phibsborough.
Convicted drug dealer Douglas (55) was lucky to survive when he was shot numerous times on the evening of last November 8, only 100 metres from his home.
The father-of-one spent several weeks in hospital after the botched shooting on Killala Road.
He was readmitted in December after he suffered infections to his wounds.
In 2010, Douglas was sentenced to 10 years in prison with five suspended in connection with the seizure of €562,000 worth of cocaine in April 2008.
The drugs that Douglas was caught with are understood to have been trafficked here by the Kinahan cartel.
Detectives from the Garda National Drugs Unit arrested him and three other men on April 13, 2008, after a surveillance operation was set up following a tip-off.
They were stopped in a taxi in the Pearse Street area and a holdall bag containing 8kg of cocaine was recovered.
Douglas was previously close to aviation broker John Kinsella (46), who was released from prison in 2014 after serving a 10-year sentence for conspiring to import drugs.
Former super heavyweight national boxing champ Kinsella was caged for trying to smuggle €7m worth of drugs into the country through Weston Airport, Leixlip.