Mr O’Neill, 42, from Drimnagh in Dublin, who was known to friends as Nailer, was enjoying a family holiday with his partner and three children in the Spanish island resort of Costa de la Calma to celebrate his birthday, when he was shot dead on August 17.
It is believed the gunman was targeting a member of the Hutch family as part of the Kinahan-Hutch feud, who Mr O’Neill happened to be talking to at the time.
Mr O’Neill was the 10th victim, and the second innocent victim, of the spate of bloody violence linked to the feud.
Last night’s Prime Time programme on RTÉ showed footage of an alleged gunman running past a shop’s CCTV camera in one direction and then back in the other direction 30 seconds later after shooting the Dublin City Council worker in the street.
It is believed the attacker may have been in his late 30s and escaped from the scene in a vehicle.
The programme also interviewed a senior member of the Spanish police, which is investigating the Kinahan gang.
He spoke on the condition of anonymity and said police there had been sharing information with gardaí about Irish criminals based in Spain.
He said the Kinahan crime gang was the subject of a major international investigation.
“The Kinahan clan has been settled on the Costa Del Sol for a number of years, and they are one of the most relevant and dangerous criminal organisation operating in Europe,” he said.
“They are mostly integrated and made up of Irish, British and Spanish citizens and they are involved in drug trafficking, arms trafficking and money laundering among other criminal activities.
“Ireland has provided with a lot of intelligence about these criminals. And we have obtained good information in Spain in order to complete a full picture of the gangs.”