Pope Benedict XVI’s decision to become the first leader of the Catholic Church to resign since the Middle Ages has left a slew of unanswered questions.

In an official statement, Pope Benedict blamed his resignation on advancing years, saying declining health had left him unable to properly lead the world’s 1.2 billion Catholics.

“Having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine ministry,” he said.

An official spokesman later added that the Pope is suffering from a “decline in vigor, both of the body and spirit”.

To a degree, that’s probably true. Italian newspapers have revealed Pope Benedict suffered a “serious fall” this year and underwent heart surgery in November to replace a pacemaker fitted after an earlier heart attack.

But in a world governed by tradition, serving Popes don’t step aside, no matter how ailing.

Pope Benedict’s predecessor, John Paul II, served for 27 years, surviving an assassination attempt. After being diagnosed with Parkinson’s in 2001, Pope John Paul II suffered severe difficulties speaking and even sitting up. But he carried on until his death in 2005.

The last pope who failed to carry on until the bitter end was Gregory XII, who was forced out in 1415.

The last to go voluntarily was Celestine V, who resigned in 1294.

But if the fact of the Pope’s departure is unusual, its timing looks downright suspicious.

The Vatican claims Pope Benedict had been considering the move for almost a year, praying intensively as he decided whether to quit.

But if so, why did he recently allow officials to schedule an official tour of Brazil for July?

Why, too, insiders wonder, shortly before Christmas did Pope Benedict promote one of the Vatican’s most glamorous figures, fellow German Georg Ganswein, to Archbishop and the high-profile position of Prefect of his Pontifical Household?

At the time of his appointment, 56-year-old Georg Ganswein – who is known as “the Black Forest Adonis” and “Gorgeous George” on account of his good looks – was billed as the perfect right-hand man to protect an ageing Pontiff from the daily grind of Vatican politics.

Georg Ganswein then appeared on the cover of last month’s Italian Vanity Fair, billed as the “George Clooney of Catholicism”.

The article pointed out that papal aides are promoted to archbishop when an ailing Pope wishes to create an unofficial “gatekeeper”. But if Pope Benedict knew he was about to quit, why appoint Georg Ganswein to this position?

The Pope’s resignation also comes at a time of scrutiny over the Vatican’s alleged links to the world of organized crime.

Pope Benedict XVI’s decision to become the first leader of the Catholic Church to resign since the Middle Ages has left a slew of unanswered questions

Last summer saw the scandalous trial of Paolo Gabriele, Pope Benedict’s butler, who was sentenced to 18 months in prison for stealing confidential documents from his master’s desk and passing them to a journalist.

The papers were given to Gianluigi Nuzzi, a reporter whose “Vatileaks” scoop alleged corruption at the Vatican Bank, including the laundering of $250 million on behalf of the Mafia.

In the wake of Gianluigi Nuzzi’s revelations, the bank’s president was forced to resign. A replacement is due to be announced in the coming months.

His identity is of great concern to organized criminals, who fear the “wrong” appointee will attempt to wipe clean the tarnished bank’s slate by confessing a raft of previous financial misdeeds.

Pope Benedict was expected to usher in just such a new broom; his successor may not. The fact his departure is good news for the mafia has left many suspicious.

But the most curious figure in the shock resignation is Cardinal Angelo Sodano.

Pope Benedict XVI and Cardinal Angelo Sodano are hardly allies. Indeed, for years they have been regarded as bitter rivals, clashing repeatedly as they each climbed the slippery pole of the hierarchy.

Months after Benedict became Pope, Angelo Sodano resigned as the Vatican’s Secretary of State, its most senior political and diplomatic post, after 12 years in the high-profile job. This hardly makes him an obvious candidate for a public papal embrace.

The second source of suspicion is Angelo Sodano’s professed surprise at Monday’s news of resignation.

Several Vatican insiders, including Nigerian Cardinal Francis Arinze, a top contender to be the next Pope, say Angelo Sodano learned of the coming resignation in Benedict’s private quarters the previous Friday.

If that is the case, then why did the Cardinal describe Pope Benedict’s departure, three days later, as a bolt from the blue?

And what really happened at the Friday meeting? Though held in secret, reports in the Italian press claim there was a heated argument between the men over the fraught question of how the Church should deal with clergy accused of sexual abuse.

In recent years, Pope Benedict has taken a relatively hard line on dealing with paedophile priests, an issue that has damaged the hierarchy’s reputation.

Not only has he apologized publicly to victims, he has also insisted that the Vatican, rather than individual diocese, should be in charge of investigating future abuse complaints, referring them to the police whenever possible.

Angelo Sodano takes a different view. The cardinal has been reluctant to proceed with investigations into suspect priests over the years, and famously used a prayer during Easter Mass in 2010 to describe the complaints of victims of abuse as ‘petty gossip’.

He has clashed with Benedict over this issue several times over the years. In 1995, they fell out over how to deal with Cardinal Hans Hermann Groer, who resigned as Archbishop of Vienna after being accused of molesting young men.

Benedict advised the then Pope, John Paul II, to issue an apology over the appalling allegations, which were later proven. Angelo Sodano, as the Vatican’s Secretary of State, chose to over-rule him.

Then, in 1998, Angelo Sodano instructed Benedict – then Cardinal Joseph Ratzinger – to drop an investigation into multiple counts of abuse by Father Marcial Maciel Degollado, founder of a holy order called The Legionaries of Christ. In a plot twist worthy of a Dan Brown novel, a Catholic journal uncovered evidence that Angelo Sodano had issued the order after receiving $15,000 from the order for being its “cheerleader”.

Benedict waited eight years for revenge. In 2006, he removed Marcial Maciel Degollado – later revealed to have fathered several children by different women – from his post. Angelo Sodano’s resignation from Vatican Secretary of State came soon afterwards.

Yet while it seems Angelo Sodano had several reasons to seek Pope Benedict’s resignation, that doesn’t necessarily mean he had the ability to execute such an audacious plot.

A hostile cardinal seeking to bring down a Pope would have to unearth a catastrophically devastating scandal from his past.

With Benedict’s childhood in the Hitler Youth and long career in a Church ridden with sex abuse allegations, there are avenues for attack. But eight years of scrutiny from the media has left little mud sticking to him.

There is a dubious incident from 1980, when as Archbishop of Munich he transferred a paedophile priest to another parish. And there have been complaints that during the Eighties and Nineties, in his role as head of the Vatican’s Congregation for the Doctrine of the Faith, he ignored complaints of abuse.

Getting the Pope to resign would have taken something more damning. Did Angelo Sodano stumble on a scandal? It seems unlikely.

A more plausible explanation is perhaps that constant exposure to Vatican politics had left the monkish and cerebral Benedict tired and desperate to find an escape.

“Maybe an unpleasant meeting with Sodano pushed him over the edge,” says a veteran insider.

“The Vatileaks scandal showed the place to be completely dysfunctional. It’s been that way throughout history.”

As for Angelo Sodano, he’s no doubt hoping one piece of Vatican history repeats itself. The last time a College of Cardinals chose a new Pope was in 2005 and Benedict was Dean of the College of Cardinals. This time, of course, the dean is none other than Cardinal Angelo Sodano.