David Yallop, Writer Who Saw a Deadly Vatican Conspiracy, Dies at 81

David Yallop, an investigative journalist who wrote popular books about true crime and conspiracy, including a best seller asserting that Pope John Paul I was murdered as part of a Vatican plot, died on Aug. 23 in London. He was 81.

The cause was complications of pneumonia, his wife, Anna Yallop, said.

Mr. Yallop’s books railed against what he saw as corruption and miscarriages of justice. They often stirred up controversy because of their explosive allegations, based on what some critics saw as inadequate evidence or vaguely sourced reporting.

“In God’s Name: An Investigation Into the Murder of Pope John Paul I” (1984) was perhaps the most controversial of all. It delved into the death of John Paul I, who was found dead at 65 in his chambers on Sept. 28, 1978, only 33 days after assuming the papacy.

John Paul was seen by some Roman Catholics as an earnest figure, perhaps ill prepared for the political machinations that faced the leader of the church. He had a history of health problems, and the official cause of death was a heart attack.

Mr. Yallop, who described himself as an agnostic Catholic, said he discovered something more sinister during several years of reporting. He argued that John Paul had been poisoned by a cabal connected to a secret Masonic lodge that had infiltrated the church and the Vatican Bank.

The Vatican, which had fueled rumors of conspiracy by issuing conflicting statements shortly after the pope’s death, called Mr. Yallop’s claims “absurd fantasies.”