The Bird with the Crystal Plumage (1970)

The killer in Argento's début applies a similar kind of love and care to the tools of that particular trade as Argento does to his own. And while the result isn't as polished as some of the Italian director's more celebrated later works, his preferred modus operandi is resolutely established; i.e. super-stylish kills with investigative portions of plot advancement in between.
The first violent act occurs in a well-lit gallery, itself framed by the entryway like some kind of grisly artwork. Like the protagonist (Tony Musante), we witness it from afar but close enough to see the knife in action.
The investigation that follows is both a device to get us to the next murder asap and something with real purpose, a means to an end for the witness.
Morricone's score is unusual in places but thoroughly effective, nonetheless.

3 harmonic intensities out of 5