The drug-dealing network which John Gilligan headed came into existence on the basis of a large loan, thought to be between £600,000 and £1 million, put up by another notorious south Dublin criminal, Martin Cahill.
The loan was made around March or April 1994, according to information which reached the Garda during its investigations into Ms Guerin's murder.
Cahill put up the money at the behest of John Traynor, mainly known as a fence and a conman. He was also Ms Guerin's main underworld contact. At various times he was close to Cahill, Gilligan and other leading Dublin criminals.
Despite his cunning and daring as a robber and gang leader, Cahill was apparently stupid enough to trust his ill-gotten earnings in a scheme recommended by Traynor. He somehow convinced Cahill to invest in a drug-trafficking operation run by Gilligan, a man who had shortly before been released from Portlaoise Prison with little or no personal capital.
It is likely that Cahill, who had become the State's best known criminal by this time, had begun to believe the somewhat exaggerated media reports of Gilligan's ruthlessness and violent reputation.
He may also have believed Traynor and Gilligan felt sufficiently threatened by his status to fear double-crossing him.
Cahill may also have liked Gilligan. They had much in common. Both rose from poverty in the south of Dublin to become successful armed robbers capable of providing their families with ostentatious lifestyles. Both were teetotal. Neither touched drugs.
Gilligan was evidently able to provide a sufficiently impressive business prospectus to convince Cahill that his investment would pay huge dividends.
Cahill had worked hard for his money. He had kept just ahead of the Garda for almost two decades with a run of increasingly precarious armed raids.
His biggest and most infamous robbery was of the Beit art collection from Russborough House, Co Wicklow, in 1986. However, Cahill was beginning to have health problems and clearly saw an end to his days as a robber. By the early 1990s, the Garda had also chased down and caught most of his gang.
Cahill, like the rest of Dublin's traditional armed criminals, made the decision to move into the relatively more lucrative world of drug-trafficking. He decided to invest his earnings in the drugs trade, seeking a high return of reputedly 100 per cent interest on his loan.
Gilligan had already forged links with the drugs trade in Amsterdam. He knew two Irish men, both former members of the Irish National Liberation Army (INLA), who had become major drug suppliers. They controlled a shipment route from Morocco to Amsterdam, either by sea, air or by road.
Gilligan had made contact with these people before he was sentenced to seven years' imprisonment in 1989 for armed robbery. He served only four years.
The international drugs trade is not based on trust between supplier and customer, however. Gilligan needed a huge cash deposit before they would start providing him with the drugs. Cahill provided the seed capital for this venture but was never to see the profits. Four months after making his investment, he was still not seeing any return on his money and was threatening to take action against Gilligan.
On August 1994, a lone gunman approached Cahill's car outside his home in Ranelagh and shot him dead.
The IRA admitted his murder. However, it is now thought that an INLA man from south Dublin accepted a large cash payment to kill Cahill - a "contract" job.
An eyewitness also described a man closely resembling Brian Meehan, one of Gilligan's closest henchmen, who was waiting for the gunman who killed Cahill.
Gilligan had assiduously worked out his trafficking operation and had invested a great deal of effort in creating his supply and distribution network. With Cahill out of the way, Gilligan's gang could enjoy all the profits of their business.
The supply route involved shipping the consignments in wooden crates using the name of a legitimate company but with a false address. These would be spotted by John Dunne, his man on the inside of a bonded warehouse in Cork. Dunne would take the boxes from the warehouse when he was alone and deliver them to the car park of one of a number of hotel or pub car parks in the midlands.
There they were collected by Meehan or one of the other three or four trusted gang members. The crates were brought to a warehouse in Dublin which had been selected and prepared by Charlie Bowden. Bowden, a former soldier, was the gang's warehouse manager and its armourer.
The drugs were then sold to a small number of customers who sold them to the hundreds of smaller dealers around the State. The drugs were finally sold at a street value of around £10 a gramme. In all, 22 metric tons of cannabis were smuggled into Ireland with a final street value of around £22 million, along with cocaine and dozens of guns. The profits were probably in the region of £4.5 million.
Gilligan compartmentalised his operations in order to reduce the amount of information any member of his gang would have. This was to ensure that if one gang member was caught by the Garda he could not bring the whole edifice down.
Thus, the collection and sale of the drugs was separated from the collection of the payments in cash from the customers. This was done by a number of gang members, including women, who passed the cash on to Russell Warren, a man with book-keeping experience whose job was to keep the accounts and launder the profits.
Warren was unable to cope with counting the amounts of cash and had to press family members into processing it.
Warren also had the job of taking cash over to the suppliers in Amsterdam. He told gardai that he rarely carried less than £100,000 on these trips.
The operation finally came to an end when the Garda received information about the warehouse at Greenmount Industrial Estate, which was used as the distribution centre, three months after the murder of Ms Guerin.
Gardai found accounts and details which exposed the entire operation.
The warehouse also yielded up fingerprint and forensic evidence which linked the gang to the drugs trade.