Implied
There were two versions of 'The Killer's Alphabet' that were released. The original, uncensored cut features a gruesome letter from the killer, wherein he threatens to sexually abuse the man before killing him, makes explicit sexual comments, including spelling the Word "coming" in its sexual context. The killer says he will give the man an erection and then cut off his penis. This scene was completely removed in the censored re-release and is very disturbing.
The Typographist analyses the killer's letter and speculates that he may be homosexual, and comments about the killer's "violent sexual fantasies."
*SPOILERS*
A few scenes after the killer's letter arrives, he contacts the Typographist and tells him to meet him at a park. The Typographist goes to the park, but the killer never shows up. During the scene, Vera Lynn's "As Time Goes By" is played for sexual irony, featuring romantic lyrics "Man must have his mate, a kiss is still a kiss," that are subtly linked to the killer and the Typographist's twisted relationship.
The Typographist is shown in the shower, no sensitive parts shown. During the same scene, he is shown in the mirror, his private parts obscured by fog. There is a very brief glimpse of the front of his waist, but all sensitive parts are obscured.
The killer's violent and possibly homoerotic attraction to the Typographist is implied throughout.