A 17-year-old who violently mugged a 52-year-old stroke survivor after following him on a bus has been sentenced to four years detention for this and three similar muggings.

The Romanian youth, who cannot be named as he is under-age, pleaded guilty at Dublin Circuit Criminal Court to four robberies carried out over a two-week period in April 2014, when he was just 16 years old.

Judge Catherine Murphy noted that the teenager "seemed to target vulnerable people in a cowardly manner," after she heard evidence last month.

She accepted that he was a young man at the time and no weapon was used but added “there was clearly violence used”. She said the crimes had a serious and on-going impact on the victims.

Judge Murphy sentenced the teenager to concurrent terms of four year detention but suspended the last 18 months on strict conditions including that he be subject to probation supervision for two years.

Three of the muggings involved the youth and an accomplice enticing pedestrians down the same city centre alleyway before attacking and robbing them. All the offences were carried out while he was on a peace bond.

Garda Michael McCarthy told Eilis Brennan BL, prosecuting, that the two youths followed a stroke survivor as he travelled on Dublin buses on April 8.

The man noticed the two teenagers after he got off a bus on O'Connell Street. After changing to another bus, he saw that the two youths had also switched buses and were sitting much closer to him than before, making him very uncomfortable.

The victim was on downstairs seats allocated for disabled passengers.

He got off the bus on Booterstown Avenue shortly before midnight and was struck on the head from behind, causing severe lacerations, bruising and marked swelling around his eye.

In a victim impact statement, the man said he'd been “left for dead” and would have died were it not for his neighbours who came to his aid.

His briefcase containing his thesis which he'd worked on for six months was stolen and never recovered.

He said he had been in a wheelchair in 2011 and had only since relearned to walk, adding that he was “utterly vulnerable” and could not run.

The youth and his co-accused further admitted robbing a man on 20 April in an alleyway at Crampton Court, Dublin 2.

The two youths spoke to the man on Georges Street, then knocked him out and robbed his watch, two smartphones and €300 in cash. In total, €2,700 of his property was robbed and never recovered.

CCTV footage from the Olympia Theatre showed the accused punching the victim and stamping on his face as he lay unconscious.

In his victim impact report, the man said the crime has altered his whole life and he is “constantly looking over his shoulder”.

He avoids the city centre and remains very nervous to go anywhere alone, taking taxis even for short distances.

In the early hours of April 24 the teenager mugged a 65-year-old homeless man, after inviting him to come and look for food.

The homeless man said he was “kind of lost” when two youths took him up the same alleyway, attacked him and robbed €300 in cash. CCTV footage showed the accused stamping on the man's head five times.

On April 17 the youths attacked a 46-year-old victim to the ground before attacking him. The man suffered cuts to head requiring six stitches, a fractured nasal bone, a black eye and amnesia.

The youths also robbed €170 in cash and two silver rings worth €800.

Victim impact reports were unavailable for these last two victims. The 17-year-old youth was arrested and has been in custody since April 26. He has seven previous minor convictions.

Defence counsel David Wheelahan BL said the teenager moved to Ireland in 2010 and wanted to apologise to his victims.

He said the youth has no history of violence but was fortunate not to be before the court on more serious charges.

Counsel said the teenager displayed naivety by returning to the same place three times to commit the crimes in a short time period.

He said the teenager is engaging well in St Pat's where he is a “model detainee”.

The co-accused youth who pleaded guilty to some offences will be sentenced on January 26 next.