* AdaptationDisplacement: Many people aren't even aware it's based on a novel. Even though he was a prolific writer of crime fiction and true crime, Arthur La Bern is largely forgotten except for having his book ''Goodbye Piccadilly, Farewell Leicester Square'' turned into this film.
* CompleteMonster: Bob Rusk, despite his veneer as a [[FauxAffablyEvil kind-hearted, jovial, and upstanding citizen]] and good friend to [[AntiHero Richard Blaney]], is in actuality a sexually sadistic psychopath who moonlights as the infamous "[[SerialKiller Necktie Murderer]]". Rusk rapes and then strangles his female victims with his tie, proclaiming that "[[HeManWomanHater all women are the same]]" and denouncing them for not fulfilling his perverse urges. Revealing his true colors to Richard's ex-wife Brenda, Rusk [[RapeAsDrama forces himself on her]] before violently strangling her to death. Rusk later lures Richard's lover Barbara to her death, and uses the dead woman's clothes to frame his old friend for the murders. When confronted by Richard and Chief Inspector Oxford, Rusk is in the process of disposing of the corpse of yet another victim. Completely bereft of compassion and remorse, Bob Rusk is only able to mask his true self with superficial charm, and deep down is an utterly callous and twisted individual who kills for his own pleasure.
* GeniusBonus: Not only does someone comment "We haven't had a good, juicy series of sex murders since [[https://en.wikipedia.org/wiki/John_Christie_(murderer) Christie]]", the basic storyline is almost identical to the [[Film/TenRillingtonPlace John Christie]] case: a FauxAffablyEvil SerialKiller successfully frames an acquaintance, but the police belatedly start investigating him.
* JerkassWoobie: Richard Blaney, he's definitely TheMeanBrit, but is WronglyAccused of being the Necktie Killer and lost the two women in his life who understood him, Brenda and Babs, to the real killer - his own friend Rusk.
* {{Narm}}: The tongue sticking out. Apparently meant to accentuate the horror of the scene, but it just looks comical. But given who the director was and the BlackComedy elsewhere in the film, this might be the IntendedAudienceReaction.
* PoorMansSubstitute: Barry Foster is very reminiscent of Creator/MichaelCaine, who turned down the role of Rusk when Creator/AlfredHitchcock offered it to him.
* RewatchBonus:
** The scene where Blaney visits Rusk at the fruit market after losing his job at the pub. On first viewing, it's just some exposition about Blaney and his life. On rewatch, when you pay close attention to Rusk, he seems to be dropping hints about his intentions. He's the one who suggests to Blaney that he should see his ex-wife, and he also says something about how beautiful Babs is. Rusk may have been planning his next murders and the framing of Blaney for a while.
** Since we don't really learn Rusk's last name until later in the film, on first viewing we don't catch the significance of Brenda calling him Mr. Robinson when he shows up at her office.