Gardai have launched a murder investigation following the death of a 20-year-old man.
The man was found on the Old Blessington Road in Tallaght on November 1 at about 3am.
He had serious head injuries and was removed to Tallaght Hospital and then Beaumont Hospital.
He died as a result of his injuries today.
A Post Mortem was carried out and the investigation has now been upgraded to murder.
A 20-year-old man was arrested in the Tallaght area this afternoon and is being held at Tallaght Garda Station.