THOUGH the rantings of the young woman in the dock were sensational, they were pretty much par for the course in a busy city courthouse inured to the constant outpourings of the mad, the bad and the sad.

But, for once, the police officer on duty at Glasgow Sheriff Court could not quite dismiss the fantastic claims being made by Joyce Osagiede, a West African asylum seeker living in Pollokshaws. She talked of black magic, of dark, unspeakable powers, of human sacrifice and of how her own son had been the victim of a ritual killing.

As PC Jim McGlynn, a member of Strathclyde Police's child protection unit, listened to the lurid details, his policeman's instinct kicked in. He recalled a case he had read about recently in the national press. The torso of an unknown black child - detectives named him ''Adam'' - had been found floating in the Thames near Southwark Bridge. The suspicion was that he had been the victim of a ritual killing.

The constable contacted the murder squad in south London. It was one of those ''It's probably nothing, but . . .'' calls. It turned out to be the breakthrough the Metropolitan Police had been waiting for, as much in hope as in expectation. That phone call, made in January 2002, sparked off a remarkable chain of events which led the detectives to the murky edges of Hamburg, to the street markets of Nigeria, and ever closer to solving the mystery of Adam's death.

The case of the torso-in-the-Thames is one of the most engrossing true crime tales of modern times. Faced with nothing more than a limbless, headless corpse - no identity, no crime scene, no suspects - the investigation team was forced to think out of the box. To explore far beyond the standard terms of evidential reference. Along the way, they extended the boundaries of forensic science.

Ms Osagiede presented herself and her two young daughters to immigration officials in Croydon in December 2001, claiming asylum. Exactly how long she had been in the UK before that, no-one knew for sure.

She said that she had originally come from Sierra Leone but had been living most recently in Nigeria. Caught up in a ritual cult, she had fled the country. Her husband, she claimed, had been a leading light in the group which had been involved in demonic rituals, including human sacrifice. She said he had played an active part in the deaths of 11 children. One of them, she said, had been their eldest child.

She told the immigration officers that, by leaving the cult, she had put her own and her surviving children's lives in mortal danger. Based on her claim, she was dispersed to Glasgow where she moved into a flat in the south side.

Detective Sergeant Nick Chalmers, who has been involved in the Adam case from the start, said: ''Her two daughters were taken into care because there were suggestions that she had become involved in prostitution once she arrived in Glasgow.

''The police went to her house, found the kids were not being cared for and they were taken to a place of safety.''

Then, on Hogmanay 2001, Ms Osagiede did a most peculiar thing. She walked into her local social work department in Pollokshaws and asked to get her children back. Not, on the face of it, an entirely unreasonable request from a mother on New Year's eve.

But then, amazingly, she freely admitted that she wanted them back so that they could take part in a ritual ceremony in her house that night. When the astonished social workers asked her if this was connected with the cult from whose clutches she claimed to have fled, she replied that it was.

As Mr Chalmers explained: ''It seems a very strange thing to do but you have to understand how important the power of the witch doctor is in West Africa. It is such an accepted part of life in some areas that they really believe that everyone thinks the same.''

However, once Ms Osagiede saw how shocked the social workers were, she began to change her story. But it was too late. So concerned were the officials that they took her to court to gain an order from a sheriff preventing her from having any access to her daughters.

That was when Mr McGlynn entered the picture.

Mr Chalmers, the murder squad officer who came up to Glasgow to interview her, recalled: ''My first thoughts were that I was going to see a woman who may have suffered a similar fate to the parents of our victim. If she was familiar with human sacrifice, the motives behind it, and the effects it had on families, then it might help us understand. After all, it appeared that she had a child, about the same age as our victim, who had been ritually killed.''

But, when he first interviewed her in Glasgow, Mr Chalmers very quickly realised that Ms Osagiede knew a great deal more than she was saying.

''Frankly, she was not as co-operative as you would expect from someone who was a victim. She refused to give a DNA sample. She wouldn't go in to detail about her own son's death. But she did talk in general terms about ritualistic practices and it became quite clear she was familiar with those practices,'' he said.

The detective did get one positive lead from the interview. As he spoke to Ms Osagiede, he noticed, lying on top of her handbag, a Blockbuster's video card bearing an address in Catford, south London. He went to that address.

''The woman at the house remembered that Joyce, just by chance, had knocked on her door and said that she was looking for someone at a nearby address. She had probably stolen the video card when she was inside the house.

''The woman recalled that Joyce had said she had been living in Germany prior to coming to England,'' said Mr Chalmers.

The German connection was of vital significance. Adam's torso had been dressed in a pair of distinctive orange shorts, labelled Kids and Co. Not only were the shorts retailed exclusively in Germany, they had gone on sale just a few months before Adam's murder.

The detectives applied for a warrant to search Ms Osagiede's flat in Glasgow. There they found items of clothing from Kids and Co, the same size as the shorts found on Adam. The clothes were female - but so too were Adam's shorts.

Joyce was taken to London for questioning. However, though there were numerous inaccuracies in her story, all the police really had was a series of coincidences. Eventually, they were able to secure a DNA sample. Joyce's DNA did not match Adam's.

There was nothing to justify charging her with any offence. Because of the publicity surrounding her case in Scotland it was agreed that she could not go back to Glasgow. Around the same time, however, the detectives went to an address which they knew Ms Osagiede had visited in Lewisham. There they found her Nigerian passport, confirmation that her claim to having been born in war-torn Sierra Leone was a fabrication.

The police informed the immigration service who, in turn, rejected her application for asylum. She was kept in detention, pending her deportation back to her native Benin City in Nigeria.

By now, however, the murder squad had struck gold at the German end of their inquiry. They found out that Ms Osagiede had been living in Hamburg. With the help of the local police, they also discovered details of her husband. Sam Onojhighovie was on the German police's wanted list. He had been found guilty of document forgery, a crime which may well have been connected to human trafficking.

Sentenced to seven years in prison, he had been set free briefly in order to settle his affairs (a curious quirk which the federal legal system permits). He then promptly fled.

The Adam case detectives, meanwhile, went to Hamburg and established that Joyce had been living there until just a few days before she turned up at the immigration service in Croydon in December, 2001. This tended to support the view that she had not been actively involved in Adam's murder (his body had been discovered in September 2001).

However, they also discovered that the Hamburg flat where she had been living had not been relet. It still contained all the clothing she had left behind.

The detectives showed neighbours and contacts in the German city a pair of orange shorts similar to the pair found on Adam's body. One woman confirmed that they were similar to the ones which she had seen Ms Osagiede's elder daughter wearing.

Back in London, the police reinterviewed Ms Osagiede. Mr Chalmers recalled: ''She accepted that she had bought from Kids and Co a pair of orange shorts. 'Where are they now?' she was asked. 'In my flat in Scotland,' she said. They were not. Then, 'I left them in the house in Germany.' No, they're not there either.

''Then she tried to say that she'd given them to another woman in Germany just before she left. Everything we have done is on the assumption that those are the shorts that were found on our victim.''

The police still had no reason to detain Ms Osagiede and she was deported to Nigeria last November.

Her two daughters remain in foster care in Scotland.

The police eventually traced Mr Onojhighovie to an address in Dublin. He is currently in custody in Ireland pending his extradition to Germany to start his prison sentence.

The London detectives are content in the knowledge that Mr Onojhighovie is accessible to them, if and when they need him. There seems little doubt that they will.