DUBLIN — The police are investigating the gangland-style execution of a former senior figure in an Irish Republican Army splinter group, who was ambushed from behind by two masked gunmen in the southwest city of Cork.

The victim, Aidan O’Driscoll, 37, known as “the Beast,’’ died in a hospital a few hours after the attack Wednesday in Cork’s Blackpool neighborhood, where the assailants shot him once in the back and twice more in the head as he lay on the ground, witnesses said.

It was Ireland’s first such killing in four years and stunned the residents of Cork, who are unaccustomed to such violence.

Two burned cars were found nearby, believed to have been used by the assailants, who apparently set them afire to destroy evidence, a standard practice of the IRA during the height of its political violence.

O’Driscoll had long been linked to criminal elements, leading to numerous theories about the identities of his killers. But the police said Thursday that it was premature to draw any conclusions.

He was known to have enemies among drug dealers, gang members, and within the outlawed IRA splinter group he had once briefly helped lead, the Real IRA.

The group derived its name from having rejected the formal disarmament of the IRA after the 1998 Good Friday agreement aimed at ending the strife in Northern Ireland.

O’Driscoll first made headlines in 2005 when he was sentenced to three years in prison for membership in the Real IRA. The conviction was overturned in 2008, but he was reported to have grown close to Alan Ryan, a former Real IRA leader, during his imprisonment. The two began to collaborate when Ryan began a violent campaign against drug dealing gangs in Dublin.

The Real IRA justified the violence as an attempt to rid Dublin of drug dealers, but some viewed it as extortion. Drug dealers were forced to surrender hundreds of thousands of euros to avoid retribution. Ryan was shot to death in 2012.

O’Driscoll was then believed to have been appointed head of the organization, but he was forced out within a year. He was shot in both legs by fellow Real IRA members who had accused him of skimming profits from smuggling and other crimes.

In 2015, he was arrested and questioned about what the authorities called the crucifixion of a trader from Limerick after a dispute over a business deal. The trader’s feet had been stapled to the ground with a nail gun.

O’Driscoll denied involvement and was never charged.

O’Driscoll’s nickname is believed to have been derived from his days as a soccer player in the Gaelic Athletic Association. He had been a well-liked member of Delanys, the local club in Cork.

The club secretary, Denis O’Flaherty, said O’Driscoll had been a highly committed and “very talented player.’’

Others expressed similar shock. A local member of Parliament, Mick Barry, described the Blackpool area of Cork as a “relatively quiet working-class community’’ where such crimes rarely happen.