The scene where cousins Mark Noonan and Glen Murphy were shot dead

GARDAí are exploring the possibility that two young men shot dead on Tuesday may have been murdered in a case of mistaken identity by a north Dublin crime gang. A source said this theory was not definitive, but so far detectives have failed to find any other clear motive for the double shooting.

Cousins Mark Noonan (23) and Glen Murphy (19) were not involved in gangland criminality. They were shot dead on Tuesday night at the Tesco Clearwater petrol station in Finglas. Gardaí believe that a Coolock gang carried out the well orchestrated shooting. Gardaí have been exploring who could have wanted the young men killed and have failed to unearth any reasons for their murder.

"We have established that they have not gotten on the wrong side of major criminals that would justify them being shot dead. We didn't initially believe it was mistaken identity but it is being explored now as a possibility," said a source.

Neither of the victims were known to gardaí for any involvement in organised crime, although Murphy had served a short prison sentence for criminal damage. Detectives investigating the double murder initially did not believe it was a case of mistaken identity as the hit was so well organised. But they have received intelligence that a Coolock gang, involved in the sale and supply of heroin and cocaine, intended to murder two other men – although the intended targets' identity has not been specified.

Another motive being explored is whether the cousins could have owed a significant amount of cash to the Coolock drug gang, but gardaí have not established that they were in debt to any gang. Gardaí have been examining whether the cousins could have been involved on the fringes of any gangland murders, but so far have no concrete evidence pointing them in this direction.

Murphy and Noonan had been at a female friend's apartment on Rathbourne Drive, Finglas, on Tuesday night when they decided to go out for cigarettes. They drove in Noonan's car to the Tesco petrol station at the Clearwater shopping centre on Finglas Road, arriving just after 11.40pm. They parked their car and both walked towards the service hatch. A BMW 5 series – which was laying in wait – carrying three men pulled alongside. Two occupants, sitting in the front passenger and back seat, opened fired on the men from the moving vehicle with automatic pistols.