It was an intruder. It was a kidnapper. It was her mother. It was her brother.

Everyone has a theory about the murder of JonBenet Ramsey. Now, at last, America may discover the terrible truth

Investigators tracking the killer of six-year-old JonBenet Ramsey, the former child pageant queen from Boulder, Colorado, have never had much to work with. They do at least have the scribbled ransom note found in the home of her parents, Patsy and John Ramsey. Asking for $118,000 for the little girl, the message included this warning to her father: "Don't try to grow a brain, John." There was no need for Mr Ramsey to agonise over the note. Hours after JonBenet was declared missing on 26 December 1996, he forced open a jammed door in the basement of the Tudor- style house and found the limp body of his daughter, bludgeoned, garrotted and possibly sexually molested. Two years later, no arrests have been made and people are wondering: is it the police who have failed to grow a brain?

This week, a grand jury, first assembled in Boulder last September to sift through what scant evidence there is, resumes its work after a month's break. This time, the grand jury will not stop until it can do no more: either they will admit defeat and the JonBenet murder trail will be left to go cold, or charges will be filed and the way will be opened at last for a trial.

An entire nation is agog, and everyone has a dinner-table theory. Was the killer an unknown intruder, as Mr and Mrs Ramsey, through their lawyer, continue to insist? Or could JonBenet's elder brother, Burke, just nine at the time, have committed so heinous a crime? Or was it the parents - or just one of the parents - who smashed the skull of the former Little Miss Colorado and throttled her with the garrotte? The couple now live 1,200 miles away in suburban Atlanta. As the only people identified by the Boulder authorities as under an "umbrella of suspicion", they know that their fates are in the balance. Both are expected to testify very soon before the grand jury, on the events of that night.

Few crimes this century, with the obvious exception of the trial of the football star OJ Simpson, have so fascinated the American public. For two years, the story has been a front-cover staple of supermarket tabloids and news weeklies alike. Barely a night passes without haunting footage running on America's television screens of the perky tot, all golden hair and sparkling eyes, treading the stage on the junior pageant circuit. Whole continents of the Internet are dedicated to web pages on the mystery.

At the heart of the media coverage is one constant theme: a frenzy of criticism of the Boulder police and the city's benighted district attorney, Alex Hunter. Bungled detective work in the investigation's first hours created an image of the Boulder police team as clones of the Keystone Cops. So, too, did a string of angry resignations in Hunter's police team last year. Above all are the suspicions that, because of their wealth and high standing in Boulder society, the Ramseys have received kid-glove treatment. John Ramsey, 55, made a personal fortune when several years ago he sold a computer business, and is now building another computer company in Atlanta. Patsy Ramsey, 41, is herself a former beauty queen from West Virginia. Together the couple seemed to represent the quintessential American success story, with a happy home and a prosperous bank account.

Typical of the popular mistrust was this observation from Dave Ruby, an apprentice carpenter, made to me over coffee in Boulder's trendy Russian Tea Room on a recent afternoon: "This has been swept under the carpet. These were people who lived up on the hill; no one wants to touch them". Never mind that unsolved homicides in the United States are hardly rare. Indeed, roughly one-third of the murders in this country in any average year slip between the cracks of the justice system without so much as a single arrest being made. (In England and Wales the figure is 9 per cent.) This has as much to do with politics as with forensic methods. District attorneys in general are reluctant to press charges unless they are confident the case will fly before a jury. They would rather let a case drop than risk an acquittal and a black mark against their record.

But this case is different: the public has grown to know JonBenet almost as an additional family member in its collective front room, and it wants her killer found, tried and delivered to punishment. With the criticism of Hunter and the police, however, also comes widespread pessimism that that day of judgement will ever arrive. "This case seems almost frozen in time," Craig Silverman, a former Denver prosecutor, remarked last week. "All we know is that she was killed, and that a killer is on the loose. Usually, when a child killer is at large, there is a sense of urgency."

Even Henry Lee, a nationally renowned forensics expert who is serving as an adviser to Hunter, offers little hope. "We don't have much information from the witnesses. We don't have a major piece of physical evidence yet. Also, we don't have that much luck yet," he commented recently. "That's why it's extremely difficult."

Indeed, there have been setbacks from the outset. The last time the Ramseys saw their daughter alive, according to their version of events, was when she went to bed on Christmas Day, filled with excitement over the silver bicycle given to her by her parents. At 5.30am on Boxing Day, Patsy Ramsey rose from her bed and went downstairs to make coffee. She found the ransom note on the back stairs of the house, telling her that her daughter had been kidnapped and demanding the money. After waking her husband, Mrs Ramsey alerted the police. Officers soon arrived at the house, but it was only eight hours later, at about 2pm, that Mr Ramsey, after a long search through the house, found the little girl's body behind the basement door. The body remained in the house until 10.45pm that evening, when it was removed by staff from the Boulder County Coroner's Office.

Allowing Mr Ramsey to tramp through the house in search of JonBenet, and indeed to handle the body of his daughter, was the first and possibly the most serious of the mistakes committed by detectives, all from a police department that had not had to deal with a homicide in Boulder for several years. Other friends were also allowed to wander through the Ramsey home that day. That alone will be manna to the defence, should the case ever come to trial. When Boulder's police chief Tom Koby withdrew as head of the investigation in October 1997, he acknowledged that errors had been made. "If we had it to do all over again, we would do it differently," he said.

Joseph Wambaugh, the crime novelist, who is a former detective himself, noted another lapse in basic police conduct in an interview last month with People magazine - the failure of the detectives, when they arrived at the Ramsey house, to separate Patsy and John Ramsey and to question them individually. This gave them ample opportunity to co-ordinate their story. It was 30 April 1997 before the Ramseys finally submitted to a first round of formal interviews with investigators in Boulder. "It's police-school basics 101," Wambaugh commented. The problem, he said, is that "when police get involved in a case that involves wealthy, prominent people, they tend to panic." Then there is also the simple disadvantage of the passage of time. Statistically, most homicide puzzles are successfully solved within days of being committed. "As the case becomes colder, the chance is reduced," Mr Lee observed.

The cul de sac nature of the case was well illustrated by last summer's resignations. In August, Detective Steve Thomas walked out of the Boulder police department, noisily accusing Hunter of sabotaging the investigation by all but siding with Mr and Mrs Ramsey. A month later, Lou Smits, a veteran homicide detective brought out of retirement to assist with the investigation, also withdrew, declaring that the police were unfairly persecuting the bereaved parents and were blind to the possibility that the murderer might indeed have been an unidentified intruder. In his letter, he stated: "The Ramseys did not do it."

In a column last week in the Denver Post, Chuck Green, a journalist who has probably invested more ink in the story than anyone else in his profession, offered this grim observation. "If ever the public gets to fully view police conduct in the investigation and evidence in this case, it will be a sad and tragic portrait of police failures, political manoeuvring and family belligerence."

Mr Green is among those who hold little hope that charges will ever brought. But so long as the grand jury is meeting, there must still be a chance. Indeed, it is impossible for us on the outside to know just what has been given to the jury members to consider. The few pieces of information in the public domain have come via unsourced leaks of doubtful reliability, mostly given to the Denver newspapers. It would seem, however, that some progress may have been made over recent months.

The police have reportedly secured important DNA samples from the crime scene. We know that Mr and Mrs Ramsey have supplied investigators with samples of their own DNA. We are also told that investigators have secured four fibres found on the duct tape that was used to gag JonBenet, and that a match has been made between the fibres and the clothing worn by Patsy on the night of the murder. Also, laboratory work has enhanced the recording of Patsy Ramsey's first, frantic emergency call to the police, early on Boxing Day. It reportedly reveals the voice in the background to be that of her son, Burke, asking what was going on and being told firmly to return to his room. That, however, contradicts their original version of events. They said that Burke had remained asleep until the police arrived.

The key to the case, however, may yet lie with the ransom note, hurriedly written, later found to have been ripped from a pad in the Ramsey home. Running over three pages, it began: "Listen carefully. We are a group of individuals that represent a small foreign faction", and went on to demand the $118,000 in ransom money from Mr Ramsey. If popular speculation as to the identity of the killer seems to focus on Patsy Ramsey, it is because of this note. The task of analysing it was eventually handed to a professor of English, Donald Fraser, the expert who unveiled the political columnist Joe Klein as author of the anonymous best-seller, Primary Colors. Fraser ruled out both John and Burke Ramsey as possible authors of the ransom note. He could not do the same for Patsy, however, telling investigators that while he could not definitively link it to her, it bore her "rhetorical stamp".

At last we can count in months, if not weeks, the time left before we know if the slaying of JonBenet will remain a mystery or whether her killer may be brought to justice. Either way, it will remain one of the most compelling tragedies in the annals of American crime. As well as our sadness for JonBenet, another emotion has surely coloured our response to this story: a revulsion, fuelled by that video footage shown over and over on TV, at the gruesome American tradition of child beauty pageants.

If you imagine that this tale might, at least, have led to the circuit's decline, think again. The number of entrants in the All-Star Kids pageant in Colorado in 1996, when JonBenet competed, stood at 15. Since her death, People magazine reports, it has jumped to nearly 50.