Paul Halter
An article about Paul Halter by John Pugmire is at:
http://www.mysteryfile.com/Halter/Locked_Rooms.html
A two-part interview between Paul Halter and Roland Lacourbe can be found on the blog At the Scene of the Crime, translated into English by Patrick Ohl.
Part One: http://at-scene-of-crime.blogspot.com/2011/11/interview-with-paul-halter-part-i.html
Part Two: http://at-scene-of-crime.blogspot.com/2011/11/interview-with-paul-halter-part-ii.html
An interview in French, between Paul Halter and Pietro De Palma can be found on the blog Death Can Read:
http://deathcanread.blogspot.it/2013/08/entretien-avec-paul-halter-interview.html
Bibliography
La Quatrième Porte (The Fourth Door)
La Malédiction de Barberousse (Barbarossa's Curse)