The book, titled In Van Gogh's Ear: Paul Gauguin and the Pact of Silence, is the product of 10 years of research by German academics Hans Kaufmann and Rita Wildegans.

BBC: Gauguin 'cut off Van Gogh's ear'

He blames the so-called "pact of silence", which followed General Franco's death in 1975, in which an amnesty law, essentially forgiving Franco-era crimes, was approved as part of a precondition for a smooth transition to democracy.

BBC: Dig may lay Spanish poet mystery to rest