For a very compelling read, check out 'In God's Name, The Murder of Pope John Paul I' by David A. Yallop. The author is not Catholic but was contacted by people inside the Vatican and supplied with documents and information that is difficult if not impossible to get otherwise. The book is detailed and well written. Yallop is not a big fan of the Catholic Church but he for the most part is able to remain objective. The Vatican has never refuted the specifics of the book but simply issued general condemnations. Players in that book were also shielded in the Vatican, which is one reason I fear Cardinal Law will disappear there at some point and not return to America.
So little is known about JP I, but from all accounts he was a simple, humble, honest and holy man. If this story is true, then he was a martyr for the Faith. I often wonder if they exhumed his body if it would be found incorrupt.
I read the book and I think it makes an excellent charcoal starter. The Abbe de Nantes (Catholic Counter Reformation in the 20th Century)also thinks he was murdered. So, from the non-Catholic left to the extreme, insane, schismatic right, common ground can be found and comrades can embrace and unity of thought can be acheived - as long as the common enemy is the Papacy.
BTW, I know longer have the book but I recall MANY factual errors in the book