My comment was specifically about your last sentence, that his main target was physically attractive females. It's false that his only known child victims were Shapiro and Robin. "Tali S., Julie J., Monique H., and Robin Samsoe were young girls, three of whom were on their way to class, when defendant coaxed them into his automobile. Their average age was 12 years. " FindLaw's Supreme Court of California case and opinions. As far as his being sexually attracted to boys, "Defendant was released on parole in June 1977. Nine months later, defendant was found in possession of marijuana; a search of his briefcase and residence revealed photographs depicting nude male and female children." (emphasis mine) FindLaw's Supreme Court of California case and opinions. According to a woman who had an encounter with Alcala as a model and identified herself in his found photos, "Alcala showed her his portfolio, which in addition to shots of women included 'spread after spread of [naked] teenage boys.'" The Eye of a Killer As far as the book quoted by @faithx it was written by two PhDs who appear to be citing psychiatric reports of Alcala. They would likely have access to that kind of material as psychological researchers, while members of the public may not. I am sure there is a citation in the book, but I can only access the preview of the book, which does not include the bibliography. It's not wild speculation to suggest that someone who has taken (apparently, lots of) sexually explicit nude photos of teenage boys might be attracted to them.