When the commander of the Swiss Guard, his ex-model wife and a young officer in the corps were discovered shot dead at the Vatican in May 1998, it was the kind of story a journalist dreams about a mystery involving sex, death and religion in the heart of the Eternal City.

Certainly Sunday Times journalist John Follain couldnt resist, embarking on a three-year investigation which resulted in the recently-published book City of Secrets: The Truth Behind the Murders at the Vatican, the latest in a long line of accounts of alleged scandals at the Holy See.

The books less-than-explosive conclusion is that the young officer, Lance Corporal Cdric Tornay, was an idealistic admirer of the Pope who had grown increasingly frustrated at the inability of the tension-ridden Swiss Guard to protect his Holiness properly.

According to Follain, he was also devastated by the ending of a two-year affair with his commander, Colonel Alois Estermann, a strict disciplinarian who subsequently delighted in humiliating Tornay in public and was responsible for withholding his three-year service medal. And as a French-speaking Swiss in a corps dominated by German-speaking compatriots, he had no support network in either the guard or the Vatican to turn to. All of these factors, Follain believes, combined to push the troubled soldier to murder and then suicide.

But as the author knocks down conspiracy theories one by one in the course of the book, the real story becomes not the killings themselves but the culture of secrecy and dissemblance within the Roman Catholic Church a timely subject given the child sex abuse scandal that recently rocked congregations all over the world.

The bodies of Tornay, Estermann and Estermanns Venezuelan wife Gladys Meza Romero were found in the commanders apartment on the night of 4 May 1998. Four hours later the Vatican announced that Tornay, 23, had shot the couple and then committed suicide in a fit of madness, brought on by his failure to receive a medal. This conclusion was reaffirmed at a press conference nine months later after an internal inquiry had been held.

I was amazed by the way the Vatican opened and shut the case, says Follain, an investigative journalist and author of Dishonoured Society: The Sicilian Mafias Threat to Europe and Jackal: The Secret Wars of Carlos the Jackal. The inquiry was a self-fulfilling prophecy. Loads of questions were left hanging at the press conference.

The Vaticans findings certainly failed to dampen the wild speculation that surrounded the case. Was Estermann a spy for the Stasi, the former East German secret service? Were the murders linked to Opus Dei, the controversial Catholic movement which advocates self-flagellation? Were they a crime of passion arising from a love affair between Tornay and Estermann? Or were all three people the victims of a fourth person, the real killer?

In the course of his first-person narrative, Follain speaks to Tornays family and friends, to his former colleagues in the Swiss Guard, to British experts in forensic pathology and criminal profiling, and, under the pretence of writing a general book about the city state, to Vatican insiders ranging from the spiritual adviser to the Swiss Guard, Monsignor Jehle, to Tornays confidant, the Swiss Cardinal Schwry.

The author defends his decision to lie about what he was writing in order to obtain some interviews, saying it was the only way to get in and that those he spoke to knew he was a journalist.

When people have such important things to say I think its legitimate to quote them even if they wouldnt necessarily be that happy about it, he says. At least I admit I was economical with the truth; the Vatican wont. Theyve got far more to hide than I have.

While some of the speculation about the deaths is borne out by Follains findings, some of it is exposed as wide of the mark. More interesting is the behaviour of the Holy See in the aftermath of the bloody events, as the author relates how the holy men of the cloth embarked on a damage control exercise of frightening efficiency.

Every member of the Swiss Guard was sworn to secrecy about the killings by Monsignor Jehle at seven the next morning, the author learns. A letter given by Tornay to a friend in the guard with instructions that it be passed on only to my mother, in which Tornay writes of injustices and says he is giving his life for the Pope, was confiscated by Jehle and its contents mysteriously leaked to the press before it finally reached its rightful recipient.

According to Follains book Tornays mother, Muguette Baudat, says she was told by Jehle who describes himself as the mother of the guard that her sons body was in a state of putrefaction, that his head had been torn off and that all the hotels in Rome were full, none of which was true. She believes he was trying to prevent her travelling to Rome.

Despite its inexperience in dealing with murder inquiries, the Vatican refused all help from the Italian police, barring entry to the patrol cars which rushed to the scene once news of the deaths emerged. According to Follain the autopsies on the bodies were conducted by two forensic experts who were made to swear never to talk about their work and not to keep any copies of the reports they produced.

At the end of its inquiry the Vatican released only extracts from the concluding pages of the investigating magistrates report. The names of all the witnesses, none of whom had actually seen the killings, had been omitted. Tornays mother is still campaigning to be allowed to see the report.

Follain believes that in contrast to the heros funeral given to Estermann, this failure to release the inquirys findings in full has hindered the mourning process for those who knew and loved Tornay and have yet to come to terms with his death and his crime. At least on humanitarian, compassionate grounds the Vatican should show them the files, he says.

The Holy See has, however, taken steps to modernise the Swiss Guard in the wake of the killings, and for the first time in January this year the city states annual judicial report was read in public, a move Follain believes was prompted by the scepticism that surrounded the inquiry.

A quote in City of Secrets from Tornays confidant Cardinal Schwry is indicative of the problem facing Catholics in the wake of the recent scandals that have hit the Church and the apparent reluctance of its leadership to tackle them openly. You think the Vatican is ultrapure, but when you see a religious institution like the Vatican from close up, you see its run by human beings, and well, that can be how shall I put it? discouraging, he says. You have to struggle a bit not to lose your faith.

City of Secrets is published by William Morrow and costs $25.95.

In Rome it is available at English-language bookshops.