Marc Dutroux's crimes shocked the world and left Belgium reeling. Amid accusations of a state cover-up, his case has taken eight years to come to trial. Why?

Opposite the railway line, in the shadow of a flyover, 128 route de Philippeville lies shuttered, boarded up and daubed with graffiti. Here, in this run-down suburb of Charleroi, is Belgium's house of horrors, one of the homes of Marc Dutroux, the country's most infamous murderer, rapist and paedophile, and the place that, eight years ago, yielded up the country's most appalling secret.

It was in a tiny subterranean cell beneath this small, red-brick, three-storey house that two teenage girls were discovered, cowering naked in the dark, on 15 August 1996. Freed by police, they struggled into the early evening light to tell of events that many still find difficult to comprehend.

Theirs was a story that reverberates through Belgian society to this day, and has generated rumours of a web of conspirators stretching from the backstreets of Charleroi to the residences of the Belgian royal family. In little more than a year, six girls had been incarcerated in Marcinelle by Dutroux, a man with a string of convictions who had been released early from prison after abducting and raping minors. While police bungled their investigation, four of the victims died - the youngest two apparently starving to death in Dutroux's cellar while he served a jail sentence for another crime.

On 1 March, Dutroux, his ex-wife Michelle Martin, and two associates, Michel Lelièvre and Michel Nihoul, will finally stand trial in Arlon for events that once brought 300,000 people on to the streets in protest at the authorities' failure to prevent such an extraordinary crime.

But eight years on, the questions remain. Who kidnapped the youngest girls? Did Dutroux work alone or as part of an organised network of paedophiles? And was he protected by contacts at the apex of society? Despite exhaustive investigation, a dossier of 440,000 pages and the statements of 700 witnesses, the country's most astonishing crimes remain shrouded in mystery. Only one person knows who abducted the two eight-year-old girls one summer day in 1995. That is Marc Dutroux, and he is not telling.

Julie Lejeune and Melissa Russo vanished on 24 June after stopping, just before 5pm, on the overpass of the Autoroute de Wallonie. One witness spoke of seeing two girls getting into a car; another of seeing a blonde woman with two youngsters at the same spot. To this day, Dutroux denies any role in the kidnapping of Julie and Melissa, whom he claims were brought to his home without his knowledge. But what is certain is that, by one means or another, the two girls spent the rest of their short lives in the hell of the dungeon constructed by Dutroux.

Then aged 38, Dutroux was the oldest of five children, who had left home at 16 and, after acquiring and losing a series of jobs, drifted into work as an electrician and car salesman. By 1995, he had already served part of a prison sentence for the kidnap and rape of young girls, and was well known to the police for his involvement in drugs and car theft. His underground cell, dreamed up during a prison stay, was not complete when Julie and Melissa were brought to the house beside the railway track in Marcinelle. But Dutroux converted an old water cistern into a living-space initially of just 2.34m in length and 99cm in width.

Drugged and sexually assaulted, the two girls were told that Dutroux was protecting them against his "boss" who wanted them killed, a story that helped to keep them out of sight when anyone else was in the house. Two months later, the girls were joined by two teenagers, 18-year-old Eefje Lambrecks and 17-year-old An Marchal, from the Belgian coast. They were abducted when their tram from Blankenberge stopped at Ostend, leaving them stranded - they apparently accepted a lift. According to Lelièvre, Dutroux climbed into the back seat of the car, forcing Eefje and An to swallow Rohypnol or Haldol. "He took both by the throat, and told me to pass the box of drugs. The way he held them, they couldn't cry out," Lelièvre later told an investigating magistrate.

As so often in this saga, Dutroux was nearly caught out. When his car broke down he had to persuade two Irish tourists to drive him to one of his other homes at Sars-la-Buissière before returning to the scene of the breakdown, where Lelièvre waited with the two drugged girls.

Once installed in the house at Marcinelle, the teenagers were chained up for much of the day, as well as being drugged and raped. Though Dutroux claimed that Eefje was a willing sexual partner, this hardly squares with the fact that she twice attempted to escape. Dutroux later grumbled of the practical difficulties of holding four people captive, telling his interrogators: "I had big organisational problems. I had the small ones (Julie and Melissa) downstairs, and the big ones upstairs. They could not meet each other. I told the small ones that the boss slept upstairs, and that they must not make a noise. I continued to take them to the ground floor to eat with me and to go to the toilet. When they were with me, they did what they had to do. Organising this left me practically no free time. It was a real balancing act."

After one unsuccessful attempt to get away, Eefje was stripped of her clothes to make escape more difficult. Despite making a second attempt, running naked into the street, she was recaptured by Dutroux without being spotted by neighbours. Again, Dutroux found himself within minutes from discovery. Indeed, it may have been this realisation of his vulnerability that acted as the spur for the murder of Eefje and An.

Precisely when the two teenagers were killed is unclear, because Dutroux denies responsibility. He claims that the girls were taken by a French associate, Bernard Weinstein, to whose murder Dutroux admits. But Michelle Martin, his ex-wife, presented a chilling second-hand account of the death of Eefje and An. She told her interrogators: "Dutroux told me that, by the side of the hole they had dug, one of the two girls realised that she was going to die. She even said, according to Dutroux's words, 'But I'm going to die...'."

If sexual gratification was one of Dutroux's driving forces, money was another. After his arrest, Dutroux blamed his ruthless pursuit of cash on a deprived childhood. At school, one of his sidelines was selling pictures stolen from his father's copy of Playboy. Money was probably the motive that led him to murder his associate, Bernard Weinstein, in 1995. Weinstein was threatening to return to his native France. Invited for a meal, Weinstein ate some pâté sandwiches that had been spiked by Dutroux. When he passed out from the drugs, Weinstein was manacled. Dutroux wanted to know the whereabouts of a stash of money, and was willing to use torture to find out. With metal chains secured, then tightened, around his testicles, Weinstein gave up the information required. The money was retrieved, Weinstein was drugged again, and then he was buried alive.

Meanwhile, in the cellar at Marcinelle, two young captives were awaiting their fate. In one of many police bungles, Dutroux's house was searched while the girls were there, but his explanation that the noise was made by his children (he had three) was accepted. Ironically, the best efforts of the law-enforcement authorities seem only to have sealed the fate that awaited Julie and Melissa. On 6 December 1995, Dutroux was arrested after a violent confrontation following the disappearance of a truck that he had stolen. While he served a four-month prison sentence, his young captives were left with little food or water. Lelièvre shirked the task of ensuring that the girls stayed alive. Michelle Martin, who was living elsewhere at the time, says that she was too scared to go down to the underground cell. She paid only brief visits to the house in order to feed Dutroux's two dogs, Sultan and Sheera.

Dutroux says that when he emerged from prison in March 1996, the two girls were either dead or dying. He professed acute distress, and claims to have tried desperately to revive Melissa (Julie was already dead, according to his version). Yet he seems to have waited for hours before even entering the cellar, busying himself with other activities. According to Martin, Dutroux's first actions when he entered the house at Marcinelle were to make her clear up the excrement left by the two dogs, and then to rape her. The two emaciated bodies of Julie and Melissa were buried later at Sars-la-Buissière.

Marc Dutroux had now been kidnapping and raping minors for more than a decade, and had a criminal record dating back to 1979. In February 1985, he had been arrested for five separate incidents of rape and kidnap of girls aged between 12 and 19. Though sentenced to more than 13 years, he served only three.

Yet still, despite the disappearance of four girls, he was at large. On 28 May 1996, 12-year-old Sabine Dardenne disappeared while riding her bike to school at Kain near Tournai. She was to spend 79 days at Marcinelle, much of it in the cell she called "the hole". Her testimony reveals that the torment inflicted by Dutroux on his victims was not just physical, but psychological as well. Sabine was told to write to her family, and sent anguished appeals in letters destined to go no further than her captor. Dutroux used the information gleaned from her writing to deploy more psychological pressure on the 12-year-old. Sabine was told that her parents had refused to pay a ransom, and that Dutroux was protecting her from his "boss" who wanted her dead.

On 9 August, Dutroux made his final abduction. Laetitia Delhez was taken from near a swimming-pool at Beatrix, close to Neufchâteau. But this time there were witnesses, including one youth who was so worried that his bike was about to be stolen by the driver of a mysterious van that he memorised three numbers on the registration plate.

Laetitia spent six days at Marcinelle, waking from a drugged stupor to find herself in chains. Not only were she and Sabine raped, they were manipulated into believing that they were a threat to each other. By now, the dungeon was larger, but in August it was stiflingly hot because of the proximity of the water-heater. In six days, Laetitia subsisted on bread, apples, a little cheese, sugar, jam and bottles of water.

But the net was finally closing, because the number plate had been identified. Picked up by police, Dutroux finally cracked on 15 August, and took the investigators to Marcinelle. At 6.30pm, he moved the boxes and bottles of water that concealed the entrance to the underground cell. "Inside there were two girls," the police report says. "They were naked and pressed into a corner. They panicked. They did not believe that this was the police. 'Is it true?' the girls asked. We reassured them. Sabine said several times, 'It's true, I'm going to see mother again'."

With the sensational news of the girls' rescue, Belgium woke, with a jolt, to the scale of the crime. But for the parents of Julie and Melissa, An and Eefje, this fleeting moment of hope turned to agony as Dutroux finally revealed where their daughters were buried.

Eight years on, Belgium is still haunted by the case. As Herman Van Rompuy, vice-premier at the time, puts it: "It still casts a shadow over [Belgium]. How can something like that happen in our society? People are still asking, is there something else behind it?" Not least, questions remain about how the suspect evaded the authorities for so long. The arrest of Nihoul, a police informer and fixer, with low-level political contacts, has fuelled theories that investigators laid off because Dutroux had highly placed protectors. Nihoul is charged, along with Dutroux, of the kidnap of Laetitia, as well as drug-trafficking. He may have been trying to establish a prostitution ring.

Meanwhile, the judicial process has hardly inspired confidence. Evidence has been leaked to the press, perhaps sold by someone connected with the trial. And the length of time taken to bring Dutroux to justice is little short of a national disgrace. The questionable reliability of witness accounts could yet reduce proceedings to a farce. Who, after all, can remember accurately the events of 1995 or 1996? If the trial ever offered the prospect of national catharsis, that opportunity is long passed. Despite the lack of any new evidence, conspiracy theories have flourished. So disenchanted are the parents of Julie and Melissa that they will not be attending a hearing that they dismiss as a masquerade. The parents searched almost single-handedly for their children, distributing leaflets and posters around the country. Their disgust and sense of betrayal only grew as the scale of police bungling and lack of internal communication became clear.

By blaming Weinstein, who is in no position to give his version of the truth, Dutroux sidestepped many of the central questions. As Paul Marchal, father of An, told one Belgian newspaper: "It's easy to blame someone who is dead. I do not accept what Dutroux says. I think he does not want the truth to come out. There are things he is hiding."

Has Dutroux convinced himself that he is innocent of the deaths of the four girls, or is he protecting someone? As Marc Metdepenningen, the journalist who covered the story for Le Soir newspaper, argues: "Sometimes Dutroux seems to be playing a game. Weinstein was a permanent alibi for Dutroux. And if there was no witness, no one can prove anything. It is a matter of the story he is telling."

For families that have waited so long for justice, this presents one final, bitter irony. How much of the truth emerges in Arlon next month depends, ultimately, on one thing: the state of mind of Marc Dutroux.