Todmichel,
I haven't read BLACK ALIBI but I thought this author's summation justified my calling LM "reasonably faithful," which can mean faithful to the theme and meaning rather than just the specific plot-developments:

"Both the distinctive narrative structure and the orchestration of suspense found in The Leopard Man owe almost everything to the words Woolrich wrote. It is incredible to read Black Alibi and discover that Lewton and Tourneur’s most powerful sequences, the three “night walks” ending in death, are described in detail in the novel, sometimes just as they’ve been shot. In fact, the moment always mentioned in descriptions of the film, Theresa Delgado’s demise suggested with chilling economy by simply showing her blood trickle in underneath the door, is not the filmmakers’ at all. Perhaps the ultimate example for horror aficionados of Lewton’s less-is-more approach to screen terror appears exactly as Woolrich wrote it. Histories of the horror film continually honour Lewton’s unit for pioneering a completely new kind of horror film: the less-is-more, psychological approach to terror. But, within The Leopard Man, Woolrich’s writing deserves as much credit for the film’s technique as Tourneur’s eye and Lewton’s governing hand. "

http://cineaction.ca/issue71sample.htm