A 13-year-old boy was the first person arrested by detectives seeking the child killer of a widower gunned down when chasing a crowd of teenagers who threw eggs at his home.

Three other youths, aged 15, 16 and 18, and a 19-year-old girl were arrested soon afterwards as the hunt was stepped up to identify what Gardai (police) believe could be the youngest street gunman in Ireland.

Father of one Aidan O'Kane, 50, was shot in the stomach with a handgun in Dublin's East Wall area on Sunday. He died a half hour later in hospital.

Neighbors and cops who have dealt with the city's most vicious gangsters were especially incensed over the death of O'Kane, a mechanic who moved with his 25-year-old son into the area a year ago. He was well-liked and was said to have established a rapport with local youngsters for whom he used to mend bicycles and computers.

Gardai believe more than 10 teenagers were hanging around outside his home before the incident.

Also, O'Kane had called Gardai the night before and reported that his car had been damaged.

The killing was the 20th gun murder this year and came less than a month after Limerick rugby player Shane Geoghegan, 28, was shot dead in a case of mistaken identity.

Minister for Justice Dermot Ahern vowed to virtually wipe out handgun ownership in the state amid growing calls for a full-force offensive against the surging gun culture.

"This was a dastardly and despicable crime. The shooting underlines yet again how we have to crack down on handguns in our society," said Ahern.

"My legislation banning the massive growth in ownership of legal handguns is pushing ahead. I intend to remove the 1,800 legally held handguns as soon as possible, and I know Gardai continue to seize significant numbers of illegal handguns.

"I know from talking to senior Gardai that handguns continue to pose a major threat, and both myself and the Gardai will continue to crack down on their use."

Main opposition justice spokesman Charlie Flanagan of Fine Gael urged the government to back his party's calls for 10-year sentences for those convicted of carrying weapons, and the creation of a new offense of not reporting lost or stolen firearms or ammunition.

Flanagan added, "Other measures that Minister Ahern must bring in to stem the rising tide of violence include increased use of curfew orders, and an immediate reversal of intake cuts at the Garda training college."

Labor Party TD (member of Parliament) Joe Costello said the murder showed that "the value placed on human life is getting less and less."

He accused the government of failing to cope with the upsurge in violent crime and added, "A government which cannot protect its citizens as they go about their daily lives or relax in the privacy of their homes is seriously failing in its duty."