Can't believe the positive words said about this one above. It's a car crash of a movie taped together from odd footage with a flimsy plot, poor dialogue, slack directing and awful editing. Genuinely a new entry into my bottom 20.
So they started with Hargitay and he apparently left for America due to personal problems (Giusti explains it in the Dizionario but my Italian is not good enough to be sure of the details) and they replace him with Jean Louis. That's OK but to use footage of both actors doing the same scenes with different dubbing in order to shoe horn Hargitay's appearance in is cheapness of the highest order and actually makes even less sense of a plot which is, to say the least, pretty thin anyway.
I also don't buy the horror / giallo influences thing. There's a murder mystery but the voodoo doll element hardly qualifies it as horror and its 1966 production date makes it too early really to be influenced by giallos. There is also nothing scary or suspenseful in it that I noticed. What kept me watching was a kind of fascination as to just how it had been pieced together. The final answer was, pretty poorly.
Finally, and merely as a footnote, the DB has Peter Martell credited as appearing in this one (as does Giusti's book) but I saw no sign of him. Did I miss something or am I right in thinking this is just an error?