Mark Spellman from Knocknacree Park, Dalkey, was stabbed to death around 2am yesterday at Londonbridge Road in Sandymount.

He was walking with friends after leaving a nearby pub when they came upon a man shouting at and pushing his girlfriend. Spellman intervened to break up the row and there was a verbal exchange between the parties before the couple left.

Detectives believe the man then went to his house and got a knife, returning to confront Spellman near Lansdowne tennis club where he stabbed him in the chest. The victim was rushed to St Vincent's Hospital but was pronounced dead at 3.25am.

Gardai are stressing that the man was totally innocent.

A 20-year-old wounded in the incident is also being treated at St Vincent's. He is in a comfortable condition and gardai will interview him when they are given clearance by medical staff.

A source said: "Mark was stabbed and received a very nasty wound to his chest and there was little that doctors could do to save him. This is an absolute tragedy for the poor young man's family. This was a totally senseless murder. He was only being a good Samaritan."

Gardai at Donnybrook have appealed for witnesses to contact them on 01-6669200.