FOR 40 homes on the island of Jersey there will be, over the coming days, weeks and possibly months, no such thing as an ordinary knock on the front door. These are the homes of 40 suspects, some regarded as respected figures in a tight and wealthy island community, who are currently on a list held by the States of Jersey Police. They face arrest, questioning and possible charges in connection with physical and sexual child abuse that detectives are now convinced was systematic, endemic and brutal'' and took place over decades at one of the island's former residential institutions, called Haut de la Garenne.

We are convinced they know who they are, and are waiting for our call,'' says the calm but clearly determined Lenny Harper, the Ulsterman who is Jersey's deputy chief of police and who is heading the inquiry at the home.

But as teams of police officers, detectives, specialist anthropologists and forensic archaeologists turn a remote Victorian building above Mont Orgueil Castle into a scene from CSI, there remains the distinct possibility that Harper will find himself in charge of a larger homicide investigation.

It will be two weeks, perhaps a bit more, before the Jersey crime team are contacted by a laboratory in Cambridge. The analysis Harper is waiting for centres on the fragment of a child's skull that was dug up, buried under a concrete floor, inside Haut de la Garenne just over a week ago. Precise carbon dating of the remains may tell Harper when the child died. But there may not be enough forensic detail to tell him what he, and the rest of Jersey, really want to know - how he or she died.

Dating analysis should, however, place the partial remains at some point in Haut de la Garenne's history. First it was the Jersey Industrial School for "young people of the lower classes of society and neglected children", opened in 1867, then in 1900 became the Jersey Home for Boys, where flogging was described as "a routine practice". From 1960, as Haut de la Garenne it held juveniles on remand, orphans and children there through no fault of their own, all supposed to be cared for in an institution holding 60 children and run by around 20 residential staff till it was closed in 1986.

Finding the skull fragment at Haut de la Garenne was not an accident. If Harper's team find more remains as they methodically dig and make their way through specifically identified sites inside the building and in an adjacent field, they will have confirmed what they've been told in some detail by former residents of the home.

For over two years Harper has been conducting an investigation into allegations of what must have initially looked like a paedophile network on the island. What began covertly went public last year. Child abuse was uncovered at the island's Sea Cadets club; there were questions over brutal regimes found in some of the care institutions on Jersey.

Contacted by former residents at Haut de la Garenne who, through a confidential link with the NSPCC, told the police where to look and what to look for, a horrific picture that, Harper admits, has left many seasoned officers feeling very uneasy" has slowly emerged for what went on inside a home that was supposed to care for, not terrorise, innocent children.

From the descriptions of daily life at Haut de la Garenne given to the police and the NSPCC by some 160 victims, many who say they will appear as witnesses in court if charges are brought, there is a disturbing and brutal picture of life inside the home. There are allegations of beatings, sexual abuse, rape, hidden chambers, children drugged and then abused, of a regime of terror where daily survival was no easy task. Harper admits the picture is something society has had to deal with before - it's alarming, but not unique".

The horrors suffered by children for 20 years in care homes throughout North Wales in the 1980s and 1990s (especially at the Bryn Estyn children's home in Wrexham), which were documented in the Waterhouse Report of 2000, which investigated the offences of paedophiles trusted with children's welfare, back up Harper's view.

But Haut de la Garenne, if evidence of homicide is uncovered, may yet take such horrors to a higher level still.

From victims' testimonies there are descriptions of hidden chambers, underneath the main building, to which children were dragged to be abused. The descriptions include being chained up and mention a home-made trapdoor with stairs leading down to what any horror film would brand a dungeon.

Lawyers who have acted for child abuse victims know their clients' testimony can be unreliable, fragmented and time-distorted.

"Recollection is poor because of the emotional trauma the child was having to deal with at the time," says one leading QC with experience of trying to bring convictions in child abuse cases. "If the Jersey team have a detailed picture of what they've been told from many sources, and the excavations at the home corroborate the visual descriptions, then the suspects should be worried, very worried."

Victims' accounts describe how children at the home went missing, how staff would describe those who disappeared as simply "runaways". Harper's team have contacted some of the runaways, children who escaped the home, left the island and made new lives for themselves in places as far away as Australia and Thailand. But what records there are can't account for all the claimed runaways. Jersey's shocked population hope all the answers lie away from the island, but many seem worried that more nightmares are still to come. Rumours of buried bodies, says Harper, "can't be ignored".

At the Moorings Hotel in Gorey harbour, just a few minutes' walk down the hill from Haut de la Garenne, the scene looks like postcard perfection. With the mediaeval fortification of Mont Orgueil behind, small boats and yachts bobbing in the harbour and the Royal Jersey Golf Club just down the road, conversation in the hotel bar should be about the simple, relaxed life of the Bailiwick of Jersey, a sort of offshore Bournemouth.

Instead, John says the island doesn't like this much attention. "They the newspapers say we knew but said nothing, kept quiet." He points towards the coast and the golf club. "They took pictures of the German bunker on the first hole. Said we say nothing about how we were occupied by the Nazis. Said we notice nothing." He puts down his beer. "They can say what they like."

Vicky Coupland is the senior scene-of-crime officer at Haut de la Garenne. Working alongside a forensic anthropologist with specialist knowledge of bone fragments and a forensic archaeologist with knowledge of how rubble and debris can hold hidden meaning, Coupland is in charge of discovering what secrets may be buried at Haut de la Garenne. A sniffer dog trained to react to human remains helped the Jersey team locate the skull fragment inside the home. The dog also helped locate an underground chamber described in witness statements.

Over the coming week the focus will be on what lies beneath the home, what may lie under the tarmac courtyard, and what may be buried beneath the thin soil layer of an adjacent ploughed-up field.

Coupland says these are "difficult" crimes scenes. "We have been working in confined, cramped, dusty spaces. Lights make it hot inside a dark room where you can't stand up and where only one person can work at any one time."

Harper, from victims' descriptions, was looking for a hidden room. What has been found has staggered some of the investigating team. Worried about destroying load-bearing walls and causing damage to the main building, and fearing that evidence would be lost if they worked too fast, the Jersey team used the reaction of the sniffer dog and ground-penetrating radar equipment to discover what they thought was one underground chamber.

When they dug down and through a brick wall, they found not one chamber but two hidden rooms filled with debris. The way the room had been bricked up was not professional, indicating perhaps it had been bricked up quickly.

Victims had described being taken down to the chamber and physically abused. Harper had descriptions of a "bath" in more than one account from victims. The word "shackles" and "chains" also appeared in victims' accounts. Within days of the skull fragment being unearthed from the concrete, both a bath and shackles were said to be among the rubble from the first chamber, although Harper would not confirm either find.

What next? Within the past few days Harper's team were handed old plans that indicate the hidden chamber, though not on the routine architectural drawings for Haut de la Garenne, may in fact be part of a complex of rooms that belongs to an earlier building, with the Victorian sandstone structure built over it. Months of slow excavation may lie ahead. But there is no choice other than to go slow.

When Haut de la Garenne was converted to a youth hostel in 2004, with the old Victorian building given a £2.5 million facelift, bones were reported to have been uncovered by the workmen on the job. They were dismissed at the time as animal fragments and thrown away.

Nothing will be dismissed this time, with the investigations team hoping that some mitochondrial DNA fingerprints, which can be used to identify individuals, will be found on objects or walls in the subterranean rooms.

Records, routinely used by police on the UK mainland, seem to be absent in Jersey. In the 1960s and 1970s the States of Jersey Police had yet to be formed. The home kept what is called an "occurrence book", but according to Harper it isn't much use. Haut de la Garenne did not have its own doctor. The hospital in Jersey also holds no records of treating possibly abused children in its wards.

Harper clearly expects no help from anything written down in Jersey or at Haut de la Garenne. "The indication is that children were obstruc-ted when they tried to complain or tell someone," he says. But he is clear on one objective: what secrets the building will give up.

"We will still come away from here with evidence that children who were at Haut de la Garenne were savagely abused, abuse that involved physical and sexual assaults," he says defiantly.

Harper and the Jersey police, to be certain they are carrying out their work correctly, they have voluntarily called in a review team from the UK mainland. The Association of Chief Police Officers (Acpo) Working Group will review the investigation so far. With Jersey not being part of the United Kingdom and therefore not under Home Office jurisdiction, Harper is nevertheless keen to ensure his investigation is working by the book, even if it is someone else's.

Others believe Jersey should be looking after its own affairs, and dismiss the criticism levelled by the island's former health minister, Senator Stuart Syvret, that the "over-riding concern of the establishment is the image of Jersey and that to prosecute people would be apocalyptically bad for Jersey".

Syvret has alleged that the island's authorities have ignored past evidence of abuse of children in its care, and that, rather than charge the people at the centre of abuse allegations, they have preferred to offer them the chance to resign and leave the island. According to Syvret, who was dismissed from the Jersey cabinet in August last year, "this whole episode raises questions about the island's ability to govern itself".

Jersey's chief minister, Frank Walker, despite saying this was the time for the island to "focus its attention on the protection of vulnerable children," nevertheless found time for a press conference last week to state why Syvret had been dismissed.

"Not for whistleblowing," he said, but because Syvret had become "so abusive to other ministers that they could no longer work with him."

The egos of the two politicians are on open display when Jersey least needs this kind of contest.

In 2002 and again in 2007, Jersey held inquiries into how its childcare regime was operating. Kathy Bull, a former Ofsted official, said in her 2002 report that she had concerns about some children's services and that certain homes should be closed down. Little action was taken on Bull's recommendations, and last year another report, from Andrew Williamson, was commissioned.

His findings are to be published shortly. With international attention now on Haut de la Garenne, what Williamson says about another of the island's care homes, Greenfields, will hold particular relevance.

Williamson's focus on Greenfields will describe a harsh regime at the home, involving solitary confinement for 24 hours as punishment for boys as young as 11 years of age. The home's head, Simon Bellwood, was dismissed when he criticised what was called the "Grand Prix" system, with "the pits" a nasty euphemism for the confinement punishment.

Since then Bellwood and Syvret have said Greenfields was using "torture" on those in its care. The Howard League for Penal Reform said that had Greenfields been in England, it would have been branded as an institution "breaking the law".

If all this renewed attention on how Jersey looks after the children in its care makes the 40 suspects on the police's list think it's time to leave, Harper has a simple message for them. "There are individuals I would prefer not to leave the island" he says. "But if they leave, we will find them.