Title : El Profesor
Author : Frank McFair
Cover art : uncredited
[Madrid : Editorial Rollan, 1953. Collección F.B.I. No. 153.]
The Collección F.B.I. was a series of crime novels in the Fifties and Sixties released by the Spanish publisher Editorial Rollan. No. 153 was written by an author with the very Anglo sounding name of Frank McFair, about whom I can’t find much online, though he gets a nice representation of covers via a search in Google Images. Searching ABEBooks also reveals that he wrote quite a few mysteries in the 1950s. Apparently he contributed several of the FBI series. These novels are presumably about the exploits of the famous bureau with the same name. Given the era, could it mean anything else? Nonetheless, it's curious subject matter coming from a Spanish publisher.
Originally I thought the title of the book was just FBI; the conspicuous placement of the lettering on the cover implies as much. But no, FBI is the series. The book’s title is El Profesor. The man on the front cover might be a good guy but the sunglasses and [pasted on?] mustache give him a sinister aura. A nice Hitchcockesque touch, the reflections of the figures in the sunglasses.