'I think the percentage is very high,' says the source, identified as an Italian journalist who left the Vatican and the priesthood after he was discovered viewing gay sex websites on his Vatican computer. 'I'd put it around 80%.'
That estimate from Martel's book, which is scheduled to be published on February 21 in eight languages and 20 countries, has already made international headlines.
CNN received an early copy of the book, whose English title is 'In the Closet of the Vatican,' through a source. Neither CNN nor the source agreed to sign a nondisclosure agreement with Bloomsbury, the book's publisher in English, nor any other publisher.
While there has been no shortage of sexual scandals in the Catholic Church, mostly concerning the abuse of children, there are no reliable studies on the number of gay Catholics in the priesthood, mostly because church leaders won't allow them.
In that sense, Martel's book could have provided valuable insights. He says he talked to 1,500 sources, including 41 cardinals, 52 bishops and 45 current and former Vatican ambassadors, or nuncios, during his four years of reporting the book.
But is that 80% figure really true? And what, exactly, does 'all tendencies included' mean? Remarkably, in a 576-page book, Martel, who has written widely on LGBT culture, never returns to that estimate, nor does he try to ascertain its veracity.
Instead Martel dedicates more ink to ruminating on the presence of a rainbow colored umbrella in Casa Santa Marta, the Vatican apartments where Pope Francis and other high-level Catholic officials live, than trying to determine whether his source's estimate is true.
'I imagine the scene: its lucky owner, perhaps a cardinal or a monsignore, takes his stroll in the gardens of the Vatican with his rainbow flag in his hand! Who is he? How dare he?'
Like that passage, the book is light on verifiable accounts and heavy on innuendo. At times, it reads like French social theory translated by Page Six gossip mongers. One prominent cardinal is described as looking like a 'Viking bride.' Another is accused of having a 'flowery conversation' over the phone in a 'perfumed voice.'
Martel calls the Vatican 'one of the biggest gay communities in the world' where '50 shades of gay' lurk beneath the pious surface. This secret underworld communicates in coded messages: In Vatican parlance, he writes, to be gay is 'to be part of the parish,' an entendre that blends the sexual and sacred.
But it is unclear how Martel, who says he is sympathetic to gay clergy, supports many of his more sweeping and damning assessments. At times, he relies less on traditional journalistic methods like on-the-record conversations and documents than on his self-described 'gaydar' and coy insinuations made by secret sources. Many of those sources, he says, 'came on to me decorously.'
'It's an occupational hazard!'
That's not to say Martel hasn't touched on an important topic at a crucial time for the church. In fact, either he or his publishers seem to have planned the book's release for maximum impact.
February 21 is not only the book's publication date, but it's also the opening day for a summit the Pope has convened of top bishops from around the world to deal with the church's massive and morally damaging sexual abuse crisis.
While the Pope has tried to downplay expectations for the meeting, many Catholics around the world are expecting some sort of action or plan before it concludes on February 24.
But already Catholics have expressed concern that Martel's book, which contains some shocking but unverified allegations, will not only overshadow the church's attempts to protect children, but also essentially link gay scandals with the clergy abuse crisis.
'The timing of the book is tremendously problematic,' said the Rev. James Martin, an American Jesuit priest who has written about LGBT Catholics and the church.
'It will distract from the summit and raise in people's minds the idea that all gay priests are breaking their vows and are linked to abuse,' said Martin, who said he has read excerpts of the book.
In fact, Martel does link homosexuality to the Catholic Church's clergy abuse crisis.
'The 'culture of secrecy,' which was necessary to maintain silence about the huge presence of homosexuality in the church, has made it possible to hide sexual abuse, and for predators to benefit from this system of protection within the institution,' he writes.
Ironically, Martel's argument finds common cause with American conservatives, who have argued for years that the real roots of the clergy abuse crisis lie not in pedophilia but in homosexuality.
That charge was made most famously by Archbishop Carlo Maria Vigano, the Vatican's former US ambassador, who accused the Pope in a letter last year of turning a blind eye to the 'homosexual networks' responsible for destroying the church from the inside.
Confusingly, Martel calls Vigano's letter both 'irrefutable' and a blend of 'probable facts with pure slander.'
But ultimately the book provides little for either conservative or liberal Catholics to cheer about. Prominent figures in the papacies of John Paul II and Benedict XVI are portrayed as hypocrites, liars or sexual deviants. Some stories appear to be well-sourced, like the tale of a late Colombian cardinal who allegedly beat male prostitutes. Others are mere rumors.
And while the author has some genuinely sharp insights about the distance between the Catholic Church's public and private stances on homosexuality, they are too often buried beneath catty quotes and unverifiable anecdotes.
'From what I've read,' Martin said, 'it's hard to determine what is fact and what is fiction.'
At one point in the book, Martel asks himself why one cardinal agreed to talk to him, despite his reputation as a journalist interested in gay culture.
'Is it the attraction of the forbidden, a kind of paradoxical dandyism, that led him to see me? Or was it the sense that he was untouchable (the source of so many lapses)?'
As Martel's book hits the market next week, those are questions many of his sources may be asking themselves.
- Chanting their support for the treaty, women chanted, "The choice is ours, the decision is ours, the