Deep Red (1975) is an early film by Dario Argento and one of the best Italian films in the 20th century Italian literature and film genre known as Giallo. The reason I specify that it is one of the best Italian films is because the Italians include American films and other films from around the world in the genre, which is basically a genre that incorporates crime fiction and mystery. It can and often does have elements of horror and the Giallo movies are usually pretty steamy in the erotic department. Some examples of non-Italian Giallo are Psycho (1960) and Peeping Tom (1960).
Deep Red is about a man named Marcus Daly (David Hemmings) who witnesses the murder of a psychic (which was actually predicted by the psychic). He takes it upon himself to try and solve the case as to what the identity of the murder is. He gets close, and the people close to him start turning up dead.
Each murder begins with a creepy children's verse being sung in a la-la-la-la fashion much like the theme from Rosemary's Baby. The tune isn't just on the soundtrack of the film, it's being played through speakers at the crime scene. Marcus hears it at one point in his own apartment and knows the killer is after him, but he manages to get away. Each crime scene is also complete with primitive, scribbly drawings on the walls that look as if they were done by a child.
Deep Red is the first Argento film to use the Italian Progressive rock band Goblin to compose and perform the film's score. I once read that he originally asked Pink Floyd to do it, but they were unable. Thank goodness. Goblin went on to work with Argento a few more times and they were also asked to score George A. Romero's Dawn of the Dead (1978). Who knows, but that may not have happened if they hadn't been discovered by Argento.
Up until the late 1980's, Dario Argento made films that were highly original and genuinely surreal and terrifying. He has been called the Hyronimous Bosch of cinema and for good reason. Unfortunately, in the early 90's he either ran out of ideas or just started to get lazy. Some of his more recent films are actually unwatchable. Which is sad, because he was once a master. But Deep Red, Also called The Hatchet Murders, is Dario Argento at the top of his game and just two years before he made his masterpiece Suspiria.