Disappearance, murder and drugs - three points of a triangle. Hence the name of the police operation into the mystery of Roddy and Anne Marie Aitken, Operation Bermuda.

The detectives at Central Scotland Police, headed by Detective Chief Superintendent John Ogg, faced five possibilities when they finally learned from the family - a week later - of the disappearance of Roddy and Anne Marie.

They quickly established that Roddy Aitken was a heavy drinker and a habitual drunken driver, and that he was used to taking back roads home to avoid the police.

Although an English Sunday tabloid newspaper had stated baldly from the outset that Roddy Aitken was a drug dealer they had been, in press parlance, ''taking a flier''. There was not a shred of evidence, either from acquaintances, family or from lifestyle, which suggested Aitken was a player in the drugs trade.

The police had to work on the basis that the Aitkens were missing persons, not murder victims, and high profile, emotionally-charged appeals were made by their 20-year-old daughter, Anne Marie.

It was highly possible, given that West Stirlingshire is one of Scotland's most densely afforested regions with a maze of minor roads, that Roddy Aitken, the drunken driver, had finally run out of luck and gone off the road into a heavily wooded area,

The first priority was to mobilise all the force's available resources to search 200m either side of first major roads, then secondary roads and finally forest tracks. This took six weeks and drew a blank.

Parallel with this effort, other lines were being followed. Roddy Aitken was a wife-beater who had battered Anne Marie for many years. On one occasion he had beaten her up so severely that she had to have a metal plate inserted in her jawbone. Because of this history a possibility existed that he had finally killed his wife and gone into hiding.

As time went on, and the full extent of Aitken's drinking became known, that seemed less and less likely. He was simply not sufficiently competent most of the time to commit murder and get away with it.

The violence, the drinking and his known hatred of the police would account for the fact that the Aitkens' daughter, Anne Marie, did not report her parents' disappearance for eight days. There was also evidence in court that her boyfriend was one of her father's drug couriers.

The third theory was that Anne Marie had finally snapped, killed her violent husband, dumped his body in the forest and herself ''done a runner''.

The fourth was double suicide, though this was at the very limit of probability.

Much more likely, a third party had killed both the Aitkens and concealed their bodies. Yet there was literally nothing for Detective Chief Superintendent Ogg and his team to go on.

That theory, of course, depended on the notion that the couple - rather rowdy Glaswegians living, out of character, in a quiet Stirlingshire backwater - had been leading a double life. There was nothing to indicate, however, that in their eight years in Aberfoyle they had been living way beyond their means in the classic manner of drug dealers.

The Aitkens, originally from Drumchapel, had moved to the town after eight years in Sutton, Surrey, where Roddy had had a roofing business. It was never clear to anyone in Aberfoyle where his money came from for the drinking and the holidays abroad (they had been due to take their 13-year-old son on holiday to Cyprus on Christmas Eve but the tickets were never collected).

Detectives found that the Aitkens had little cash in the bank; most of it was spent in the one local hotel where Roddy was not persona non grata. Most pubs in the area banned him years ago.

As each possibility fell, so the ''double life'' scenario became the central pillar of the inquiry. Eventually it was proved correct - but only after a painstaking, textbook piece of detective work. When the breaks came the groundwork had been done according to best practice, so they fell into place as they should.

As the roadside searching continued, officers began putting together every shred of intelligence they could glean about the Aitkens. In line with current police practice the couple's itemised telephone bills were acquired, studied and evaluated. The intelligence data bank of Customs and Excise was also scrutinised and, from the early point when it was realised that the case had strong Glasgow connections, the intelligence arms and data banks of Strathclyde Police.

This line of investigation, analysis of telephone billing, has now become widely known, particularly from the cases of Glasgow criminal Paul Ferris, jailed for gun dealing, and of Mr Thomas McGraw who was acquitted after a jury found not proven a charge of funding a major drug-running operation between Morocco and Scotland.

Up came the name of one acquaintance whose phone number showed he was known to the Aitkens. Iain Meikleham had once been stopped at Glasgow Airport by Customs while in possession of #15,000 which was contaminated by drugs. The money had been impounded.

By now the Central Scotland Police team were acquiring itemised bills from the numbers which had appeared on the Aitken's call lists. As the networks spread the pattern which emerged was of many calls between players in the drugs trade.

Aitken had called Malaga - which just happened to be Meikleham's flight destination when he had been stopped with the money. The detectives upped the ante by studying flight manifests from Glasgow and Manchester Airports and names began leaping out from these which matched names on the growing intelligence base.

Then came one of the breaks. Eight weeks into the inquiry a man was stopped by police in the Balfron area for drunken driving and was found to have a small amount of a controlled drug in his vehicle. Again following best practice, his details were checked against the Bermuda incident room data base and up he came as an associate of Roddy Aitken.

During interview he told two Operation Bermuda detectives that Aitken had paid him to take a sum of money out to Malaga - the first hard evidence of Aitken's drug involvement.

The clinching factor was that the man described how the money had been wrapped in cellophane, then in silver paper and then with a carbonised paper, all designed to defeat airport X-ray machines. It was identical to the manner in which the money impounded from Meikleham had been wrapped.

At that point the detectives were more than satisfied that Aitken was involved in drug importation. Further checks revealed that a telephone call had been made from Manchester Airport to one of Aitken's associates - a call which created further official difficulties. Warrants are needed to check public telephone call lists.

The calls immediately before and after the Manchester call were eventually checked out. One was to an associate of Aitken in Alexandria, Dunbartonshire. The network of calls between the players was becoming wider and the analysis more complex.

The exercise was made more difficult because the numerous telephone companies could not produce itemised lists immediately. Business is not geared to police needs so the lists of calls came in piecemeal, each one requiring further analyses.

Gradually, by mid March, a picture had emerged of Aitken, the noisy drunk from Aberfoyle, and Meikleham, his associate from rural Dunbartonshire, having travelled on a number of occasions to Malaga with large sums of money. What the police could not establish was how the drugs came back into the UK.

Another break occurred, and again it came from phone billing. Police worked out that there must be a ''secret'' telephone, one which Meikleham used but which was not in his name. Having a phone in the name of an elderly relative or unwitting acquaintance, someone unlikely to quibble or raise an objection, is not an unusual criminal ploy. In this case it was obvious from the call list that it could be tied to Meikleham, although it was not listed in his name.

Then came the crunch. The last sighting of the Aitkens was at 6.45pm on December 18, 1997 at the Asda store on Milngavie Road, Bearsden.

The last indication they were alive was a call from their mobile 45 minutes later to a friend in Aberfoyle saying they would be home soon.

They were never seen again by friends or relatives. But the billing for the ''phantom'' phone used by Meikleham showed a call from it to Aitken's phone at 7.05 that night - the call which almost certainly lured the Aitkens to their deaths at Little Blairlusk Farm.

The pieces of the puzzle were falling into place.

It was not just documentary evidence which was coming to light, however. Informants were telling Central Scotland detectives that their targets were heavily involved in a major cannabis smuggling exercise.

Significantly, until three weeks before the Aitkens' disappearance, there were continual telephone calls between Aitken and Meikleham - and then they ceased. There had been a falling out. On March 23 informants were telling the Central detectives that Meikleham had disposed of the Aitkens and that Parker was involved. The arrests followed immediately.

Even with the joint resources of both Central Scotland Police and Strathclyde Police it would have been hard to have hit 40 houses and make at least 40 arrests simultaneously, so the investigators concentrated first on the main players.

Fourteen people received an early morning call at 6am. The police had at that point 38 search warrants, mostly under the misuse of drugs legislation. The net comprised 200 officers.

The inquiry had been run throughout from Central Scotland Police's Stirling HQ where Strathclyde Police had installed a liaison team. The Stirling detectives had a similar team in Glasgow.

Suspects and witnesses were taken to different locations for questioning, including Maryhill, Stirling and Dumbarton police stations. As the day progressed the story behind the disappearance of the Aitkens began to emerge, slowly, piece by piece. Then Parker cracked under interrogation and said he would take the officers to where the bodies had been burned and dumped.

When the facts emerged, that the murder had taken place in Dunbartonshire and the bodies were disposed of in Ayrshire, the whole emphasis shifted to the country's largest force.

What had begun as an intriguing Christmas disappearance puzzle for Central Scotland Police had ended up with the solution to a horrifying double murder and the smashing of a drug importation ring in Strathclyde.