Perhaps 'Torso' is the closest to a classic giallo movie in Sergio Martino's oeuvre. In my opinion, Martino, who had made four very worthy films on this subject before, just relaxed a bit.
I think that Sergio decided not to concentrate on the psychological background of what is happening, and made a real slasher, built on the well-known formula.
Small town - Unknown man kills mostly women on whom he gets aroused - A series of murders - A villa on a hill, where four girls are resting - They indulge in pleasures - He comes to them...
Sergio Martino stylistically repeated Mario Bava's 'Bay of Blood' and anticipated John Carpenter's 'Halloween' and other standard American slashers. If in Martino's earlier films, we mostly encountered calculated murders that were simply disguised as 'maniacal massacres' (with the exception of 'Eye of the Black Cat').
In 'Torso' we meet a real maniac who justifies himself with childhood psychological trauma and saws the corpses of his victims with a hacksaw.
I found the movie a bit underdeveloped in terms of psychology. Perhaps the reason is that Sergio Martino has abandoned his traditional team of actors this time - Edwige Fenech, Luigi Pistilli, George Hilton, Ivan Rassimov would have certainly strengthened the movie. The guest actors, especially the performers of the main roles did not impress me at all.
As a result: in my opinion, the whole plot structure of the movie is built to bring together in a big house the main heroine and the maniac. Moreover, the viewer for a long time does not know who exactly the main heroine is. This is done for intrigue, because we should not know who will survive the attack. Of course, not everything will be twisted, but it is obvious that this tape was inspired by many famous authors.