There are nine criminal gangs in Dublin with links to the drugs trade in the Netherlands, according to criminal intelligence reports, including one run by former associates of the gang which killed Veronica Guerin.

The three Irishmen murdered here a week ago are believed to have been involved with one of the gangs and may have been blamed for passing information to police leading to drugs seizures in the past two years.

According to Garda intelligence, 13 criminal gangs in Dublin are involved in drugs; nine of these have contacts in the Netherlands, the main source of cannabis, cocaine and synthetic drugs such as ecstasy, amphetamine and LSD for Irish criminals.

For two decades, the Dublin gangs have been placing members in the Netherlands to set up links with drugs suppliers.

The best-documented operation was that run by the gang which killed the journalist Veronica Guerin in June 1996. That gang began importing drugs on a major scale in 1994 after the Dublin criminal, Martin Cahill, put up a substantial sum to start up the business.

Cahill was subsequently killed by the gang rather than pay him what was seen as an exorbitant return he was seeking on his seed money.

The gang bought cannabis from a Dutch source who had a warehouse near Schipol Airport and it was imported into Ireland through a shipping company in Cork. There it was collected by van and delivered to the gang's warehouse in Harold's Cross, Dublin.

In three years, the gang may have shifted some £130 million worth of the drug in street value terms, where cannabis is finally sold in gramme deals for about £10. Despite being broken up by Garda action after the Guerin murder, gang members returned to the Netherlands where they attempted to restart their highly lucrative trade.

A close associate of the gang leader had tried, in the past two years, to re-establish the business and is believed to have succeeded in importing as much as tens of millions of pounds worth of the drug. However, two major shipments were seized and the gang has now been largely broken up as a result of action by Dutch and Irish police.

It is now thought possible that other members of this gang might have been seeking revenge for the police successes, which have almost certainly come about through the use of informants.

Garda sources believe that while there have been major successes against the Dublin gangs with Dutch drugs links, the illicit trade in drugs will continue.