The decision comes after a top-level meeting between the senior members of several sections of the force and the garda commissioner, Noel Conroy, following the murder last week of 22-year-old father of one James Purdue in Donaghmede.

It is understood that, in tandem with the probe of assets portfolios, including property and cars, by CAB, there will be a major increase in the monitoring and tracking of key suspects' movements in relation to drug dealing and other criminal activity.

"Arising out of the Coolock investigation that is ongoing at the moment, a number of new targets have been identified. We will describe them as 'a silent drug trafficking fraternity', " CAB chief Felix McKenna told the Sunday Tribune last week. "These investigations are now identifying small asset portfolios that these people have developed over the last five years."

Purdue's murder was the sixth violent death in the north Dublin area since February, although the current probe will focus only on the five gangland-related killings.

Gardai now face the difficult task of attempting to anticipate potential revenge attacks or any further gun attacks.

Gardai investigating Purdue's killing, outside the apartment he shared with his partner and daughter at Grattan Hall in Donaghmede, last week recovered the car used by his attackers. Gardai hope that forensic tests on the vehicle may result in a vital lead in the investigation.

Purdue, who was believed by gardai to have been involved only on the periphery of crime, died in Beaumont Hospital a short time after the shooting. The dead man was a friend of Patrick Lawlor, who disappeared in suspicious circumstances 18 months ago, although any direct link between the killing and disappearance has not yet been established, it is understood.

The Donaghmede murder comes just three weeks after a 23-year-old man was shot dead in the nearby area of Kilbarrack.

Keith Fitzsimons, from Glin Grove, was on his way to get a take-away from a local chip-shop when he stopped to chat with two other men in the garden of a house at Millbrook Road, Kilbarrack on the evening of the first Friday in June. A gunman walked up to the group and fired half a dozen rounds from a handgun. Fitzsimons was hit three times and died instantly. He was the fifth person to be murdered in the area since last Christmas, and the third to have died in a one-mile radius during that time.

The two men who were in Fitzsimons' company when he was shot dead are wellknown to gardai and are connected to local gang members involved in drug dealing and armed robbery. Both of these men were also wounded, although their injuries were not life-threatening. One of the men is believed to have been the intended target of the shooting.

Less than a week before Fitzsimons was shot, a close associate of one of the capital's biggest crime bosses was gunned down outside his Raheny home on 27 May. Fortythree-year-old Patrick Harte is believed to have been involved in the facilitation of crimes, in particular armed robbery, in the procurement of vehicles and the safe-keeping of cash. The father of four had only just returned to his home after dropping two of his children, aged eight and 10, to school.

A month before Harte's murder, a 24year-old man was also fatally shot in a gangland-style hit. Gerard Goulding, from Dublin city centre, had been lured from his home to a green area near St Donagh's Road. It is believed that whoever killed Goulding was known to him and had arranged to meet him. Shortly before he died, Goulding phoned his girlfriend, telling her that it would not be "too long" before he was home.

Just a month beforehand, gardai had launched two murder inquiries in Dublin in a six-day period. The murder of a young mother of one, Donna Cleary, who was shot dead as she attended a function at a friend's house in Coolock, was greeted with widespread public revulsion. The killing was described by justice minister Michael McDowell as a "watershed".

Taoiseach Bertie Ahern said at the time that the young woman's killing represented "a new low". He added: "Somebody to blast live rounds indiscriminately into the front room of a small house to kill a young 22-year-old mother, it's hard to think of anything more low than that. It's a very sad occasion."

Ahern called for longer sentences for serious offences such as murder. He said:

"When you see the amount of crimes and gun crimes, it just makes you feel that perhaps we are just too lenient, that people serve too short a sentence for murder."

However, it later emerged, after questions by the Irish Times to the government's information office, that the government had no immediate plans to introduce such legislation.

Cleary, the mother of a three-year-old boy, was shot dead in the early hours of 5 March. A man who had earlier been denied access to a 40th birthday party at Adare Green in Coolock, at which the young woman was a guest, fired five shots through the sitting room window. The chief suspect in the shooting, 22-year-old minor drug dealer Dwayne Foster from Finglas, later died in garda custody.

"Clearly if an automatic pistol is going to be used in circumstances such as these, we all have to reflect on what kind of society we have, " said McDowell at the time. "That applies for everybody, not just the minister for justice, it applies to the judiciary as well. Possession of firearms is a very serious offences and it must be dealt with in a way which makes an example of any offender. I regard it now as a watershed point for all our social thinking on these matters."

Attributing this type of violent acts to drug dealing, McDowell said there were provisions in the Criminal Justice Bill for a gun amnesty for illegally held weapons to be taken out of circulation.

Last month, in a media interview, the garda in charge of the Dublin Metropolitan Region North division, chief superintendent Peter Maguire, said there were now more guns in circulation than ever before.

However, the senior garda insisted that the force was winning the battle against organised crime.

Five days after Cleary's killing, a man was found dead in a lane off Blackhorse Avenue in the north inner city. It later transpired that he had been shot dead. Shea Bradley was well-known to gardai and was on bail after having been charged in connection with the shooting of a man in a botched gangland murder attempt.

A native of Derry, Bradley lived in Dublin and was heavily involved in drug dealing through a number of west Dublin drugs gangs. The dead man had reportedly claimed to be a member of the INLA. He was facing charges in relation to the shooting of a man in Pollyhops Pub, Newcastle, Dublin, in September 2005, in which an innocent man was targeted by a gunman.

The intended victim in the shooting was 22year-old Owen McCarthy, from Clondalkin, who was later abducted, brought to the Wicklow Gap and shot dead.