Donald Dewey 
Green Triangles [EPUB ebook] 

Private investigator Paul Finley is hired by an academic for the overtly simple task of returning films shot by an associate of his client in Paris more than 30 years earlier. But the contacts he is given for returning the films begin dying in various ways, including homicide and cancer. Then the client himself commits suicide. Even worse for Finley, Homeland Security agents move in to get their hands on the films.