A garda detective who shot a raider dead in an incident in Lucan last Friday opened fire after the raider put a gun to the head of a security worker and threatened to shoot him.

The Sunday Tribune has learned that a garda attached to the secretive garda National Surveillance Unit (NSU) fired five shots from his pistol hitting both Gareth Molloy and Keith Murtagh twice. The fifth shot missed its target.

Molloy, a 27-year-old armed robber from Sheriff Street in Dublin's north-inner city, died from his injuries in hospital a number of hours after the incident. Murtagh (26) also from the north-inner city, is in intensive care but doctors expect him to survive.

The shooting took place at the Centra supermarket on Foxborough Road in Lucan shortly after noon on Friday.

Members of the NSU and the Organised Crime Unit had a gang of suspected armed robbers under surveillance for five days prior to the incident.

This was part of Operation Delivery, which is targeting cash van robberies.

The six-man gang was observed acting suspiciously in the Lucan area each day and gardaí had information that they were planning to rob a Securicor van.

Just before noon, Derek 'Del Boy' Hutch, a nephew of criminal 'The Monk' Gerry Hutch and two others were observed in a stolen car following a Securicor van which was travelling close to the Centra shop.

Several unmarked garda cars followed at a distance while a two-man detail from the NSU drove to the Centra store to make sure the scene was clear.

While they were on the way to the shop, a second Securicor van arrived. This van was not scheduled to be in the area for several hours but the crew had changed their routine, as is common practice, to avoid being targeted by raiders.

As the security worker got out of the van to stock up the ATM in Centra, a car pulled up and Gareth Molloy and Keith Murtagh got out.

Molloy was carrying a sawn-off shotgun and went up behind the worker, put the weapon to the side of his head and said that if he didn't hand over the cash he would shoot him dead.

The two NSU detectives arrived at Centra and saw what was happening. They ran from their cars and shouted "armed gardaí, drop your weapons". This account has been backed up by at least five witnesses who were in the vicinity of Centra.

Murtagh turned around and fired a shot and one of the detectives opened fire, hitting each raider twice. The incident was over in less than five seconds. A forensic examination of the sawn-off shotgun later determined that there was a second unfired round in the weapon.

Derek Hutch was arrested minutes later at the Neilstown Road after his car collided with a roundabout.

The 24-year-old, who has an address in Lusk, is currently in garda custody along with two 22-year-olds from Clondalkin, and a 23-year-old from the north-inner city.

Hutch is regarded by gardaí as being involved in serious organised crime in the Dublin area.

Following the shooting, the Garda Síochána Ombudsman Commission (GSOC) immediately launched an investigation into the circumstances of the incident.

It is thought there are concerns among GSOC investigators that two men were shot even though only one was armed, although garda sources say that the incident happened so quickly that there was little time for the detective to know this once a shot was fired by Molloy.

The garda detective is said to be traumatised by the incident and has handed his Sig Sauer semi-automatic pistol to GSOC investigators for forensic examination.

The Securicor worker was uninjured but is said to be deeply traumatised and still in shock.