A viral video that shows a brutal attack on a man on the Luas was recorded earlier this month.
The graphic video, which shows a man being kicked continuously in the head, has been shared widely online in the past 24 hours.
It has emerged that it is from an incident which took place on July 6 and saw a man arrested by gardai.
Dublin Live previously reported that the man - who can be seen lying on the ground and getting kicked - was taken to the Mater hospital with serious, but non-life threatening head injuries.
The other man was arrested in connection with the incident, but was later released without charge. A file is being prepared for the DPP.
A previous garda statement said: "Gardaí attended a serious assault that occurred on Mayor St, Dublin 1 on the 6th July 2019 at approximately 6.15pm.
"Two men in their late 20s were involved in an altercation which occurred on the Luas. One of the males received serious head injuries (non life threatening) in the assault and was taken to the Mater Hospital.
"The second male received serious injuries (non life threatening) and was taken to St James hospital.
"The scene is currently preserved and investigations are ongoing."
