Pope John Paul I did not die suddenly and unexpectedly from a heart attack as the Vatican announced, but had a lonely and agonized death that could have been prevented, The Sunday Times said, quoting a new book.

John Paul I, known as "the smiling pope," died the night of Sept. 28, 1978, after a reign of 33 days."A Thief in the Night," by John Cornwell, discounts earlier theories that the pope, 65, was murdered but suggests a lack of compassion within the Vatican.

The Times printed excerpts from the book, which is to be released May 25.

Cornwell wrote that the pope was tormented by the conviction that he was unfit for the papal throne - a feeling shared by many in the Vatican - and was allowed to go to the solitary death he prayed for, untended and uncared for by those closest to him.

"The truth is much more shameful even than if the pope had been murdered. That would have been the work of several criminals or madmen, where in fact the whole of the Vatican is responsible for the death of John Paul I," Cornwell said.

Cornwell based his conclusion on his findings that the pope was convinced the conclave of cardinals that elected him had made a mistake, and that he was seriously ill before he died.

The official Vatican explanation that the pope's death was from a sudden and unexpected heart attack and he had been in perfect health was a lie, Cornwell said.

Vatican sources told Cornwell that from the day of his election, John Paul I had worried he was "usurping" the papal throne and, near the end, he was praying "a thousand times a day" for his own death.

Cornwell said the pope had been taking a medication for a serious blood-clotting condition.

"There is evidence that, not through forgetfulness, he deliberately stopped taking this medication because he could no longer continue as pope," he said.

Several medical experts said the cause of death was more likely to have been a pulmonary embolism brought about by his blood condition, Cornwell said.