Pope Francis has moved Pope John Paul I — the pope who reigned for only 33 days in 1978 — a step closer to possible sainthood.

The Vatican said Thursday that Francis had signed a decree declaring that John Paul I lived a life of heroic virtue. The Vatican must confirm a miracle attributed to his intercession for him to be beatified, and a second miracle to be canonized.

Francis signed the decree just days after the Vatican endorsed a new book debunking four decades of conspiracy theories about John Paul I's sudden death.

The book, "Pope Luciani: Chronicle of a Death," hit stores this week.

Citing John Paul I's medical file and other confidential documents, it states the former Cardinal Albino Luciani died of a heart attack.