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Pope John Paul II decided to forgive his would-be assassin while he was in the ambulance on his way to the hospital moments after being shot in St. Peter's Square, according to a new book by the Polish prelate spearheading his sainthood case.

The revelation is contained in one of the many previously unpublished speeches and memos drafted by John Paul that are contained in the book, including two documents in which he outlined the criteria for which he would resign if he became incapacitated.

The book, "Why He's a Saint" also confirms that John Paul practiced self-mortification — he whipped himself with a belt, even on vacation — and frequently slept naked on the floor as acts of penitence.

The book was written by Monsignor Slawomir Oder, the postulator, or main promoter, for John Paul's canonization cause and was released Tuesday. It was based on the testimony of the 114 witnesses and boxes of documentation Oder gathered on John Paul's life to support the case.

Pope Benedict XVI put John Paul on the fast-track for possible sainthood weeks after his April 2, 2005 death by waiving the customary five-year waiting period before the process can begin. Last month, Benedict moved John Paul a step closer to possible beatification — the first major milestone in the process — by approving a decree on his "heroic virtues."

The Vatican must now confirm that a miracle attributed to John Paul's intercession occurred in order for him to be beatified — a step which many Vatican watchers have suggested may come as early as October.

The book publishes for the first time a never-delivered speech John Paul prepared for his weekly general audience Oct. 21, 1981, five months after the Turkish gunman, Ali Agca, shot him in St. Peter's Square.

Agca served a 19-year sentence in an Italian prison for shooting the pope, and earlier this month was released from a Turkish jail where he served a 10-year sentence for killing a Turkish journalist in 1979.

John Paul had publicly forgiven Agca on May 17, 1981 — for days after the assassination attempt. And he visited Agca in prison in 1983.

But five months after the attack, John Paul prepared a lengthy treatise on the power of forgiveness and the need for it in society, using his own experience as an example.

"The act of forgiveness is the first and fundamental condition so that we aren't divided and placed one against another like enemies," he wrote in what Oder called "an open letter" on the Agca case. "It's important that not even an episode like that of May 13 succeeds in opening an abyss between two men, creating a silence that would result in breaking all forms of communication."

In the speech, he revealed that he while he had publicly forgiven Agca on May 17, "the possibility of pronouncing it before — in the ambulance that brought me from the Vatican to the Gemelli hospital where the first and decisive surgery was performed — I consider the fruit of a particular grace given to me by Jesus."

Oder speculates that John Paul decided against delivering the speech he had prepared "out of prudence" for the ongoing criminal investigation into the shooting.

The book also reports that John Paul first considered the possibility of resigning when he turned 75, the normal retirement age for bishops, going so far as to convene a group of close collaborators for an informal discussion on the topic.

He tasked then-Cardinal Joseph Ratzinger, head of the Vatican's orthodoxy office and future Pope Benedict XVI, to study the theological and historic issues implied in having an "emeritus pope."

In the end, John Paul left the question up to "providence" — he never resigned.

But he did outline on two separate occasions the criteria for which he would do so.

In 1994, he wrote what appeared to be a speech to be delivered to cardinals in which said he intended to resign "in the case of an illness determined to be incurable and which impedes the (sufficient) exercise of the function of the petrine ministry."

In a memo signed and dated five years earlier, on Feb. 15, 1989, he similarly wrote that if he was unable to sufficiently do his job because of an incurable illness, he would "renounce my sacred and canonical office" and leave it up to the top cardinals to carry out his wishes.

John Paul suffered from Parkinson's disease for many years before he eventually died of septic shock and cardiocirculatory collapse, preceded by heart and kidney failure brought on by a urinary tract infection.

Prior to his death, John Paul had been in and out of the hospital for two months and, by the end, had lost the ability to speak.