A second camera — capturing the murder from a distance — shows the gunman standing over the victim to fire a final shot into his head.
Detectives believe Luas passengers saw the early morning shooting and may be able to help identify the killer, but few are thought to have come forward.
Gardaí are trawling through cameras at Luas stops to see if they can identify any of the passengers getting off, with a view to approaching them for information.
Senior gardaí have assured people who are either unsure or fearful to come forward that they can speak to them in confidence.
Mr Kelly was gunned down on a path through a green stretch in the Rialto area of Dublin’s south inner city at around 10.30am on Monday.
The drug addict was known as a small time dealer who had operated from where he was shot for a number of years.
The father of three had a number of recent addresses nearby, including one in Drimnagh and another in the Maltings, in the south inner city.
Detectives believe he might have been lured to the spot to sell drugs at the time. The gunman was hiding in bushes on the other side of the Luas track and jumped out and ran over towards him after he made a deal.
He got close before shooting him once in the back, then across his chest, puncturing his heart, before firing a third time into the head.
Detectives suspect that a well-known criminal family from Drimnagh, linked to a gang in Crumlin, may be behind the murder.
This outfit was previously aligned to one of the two local feuding gangs, but is considered an independent crew of its own.
Detectives are investigating if there is a link between the shooting and an assault on Mr Kelly last August.
He was chased into a pub on nearby Cork St and struck with a bar stool, but managed to escape by jumping over a back wall.
After the murder on Monday, the killer put the gun in his pocket and escaped down a walkway into the New Ireland housing estate, where he had a waiting car. This car, a four-door metallic grey/lilac Opel Astra, with registration 99 LH 5711, was found partially burned a short distance away in Rialto Court.
A gun, with a silencer, was found in the car. The weapon and the vehicle are being technically examined for DNA, fingerprint, or other forensic evidence.
The suspected killer is described as 5ft10 to 6ft tall and was wearing a sky-blue hoodie with white shoulders.
He was last seen walking towards James’s Walk in the direction of the Fatima Luas stop.
Anyone with information is asked to ring the incident room at Kilmainham Garda Station on 01 6669700 or the Garda Confidential Line on 1800 666 111.