The sex industry is, in many ways, a violent and dangerous world for those who operate in it, and often exists within a grey area commonly overlooked or disregarded by law enforcement. This makes those within it easy prey for a violent criminal.
Dave is a violent misogynist with numerous issues about women, and women who work in the sex industry particular. He consequently tends to dehumanize them, making it easy for him to murder them.
Alice is a murderer who lures her male victims in by posing as a sex worker and promising sex.
Dave is a Serial Killer who targets specifically chaste women and virgins. He wants to degrade and dephase them because, in his view, any woman who ISN'T a sex worker or an easy skank is a revolting hypocrite or an aberration that needs to know her place.
The scene is set up to make it look as if Dave will murder Alice. Instead, he leaves her alone.
Alice was not a stripper, but Dave mistook her for one.
Dave changes his mind and murders Alice anyway.
It turns out Alice was a stripper, but the people that knew her did not know this because she kept it secret and / or used an assumed name for her business.
Although she momentarily escapes, Dave chases Alice down and kills her anyway.
Parodied: The heroes learn that the serial killer is soon to operate in their town. The first thing they do is to hide every sex worker in said town.
Zig Zagged: Dave's victims are murdered as a result of convenience rather than him targeting certain people; some are sex workers, some not.
Averted: Dave does not target sex workers.
Enforced: The author wishes to establish Dave as a violent serial killer without having him murder anyone the audience is intended to care about, and selects a sex worker for this purpose.
Lampshaded: "These sickos always target the girls on the street..."
Invoked: Dave explicitly decides to attack sex workers under the justification that he is cleaning up the streets.
Exploited: Dave murders Alice and several other sex workers in order to conceal another crime, both to draw attention from his other crime and because he believes that no one will concern themselves greatly over the deaths of sex workers.
Alice and her friends, fearing the risks of working the streets with potential violent killers, take measures to defend themselves and each other from those who threaten them.
Dave, realizing how pitiful Alice's life is that resulted her into a prostitute, decided to spare her.
"We're cops. We're going to deal with a dead sex worker one of these days, you'll see."
Two cops have the next conversation:
Detective Carol: "Why is it when a sex worker dies, nobody cares, but when it's anyone else, it's abig deal?" Detective Bob: "People like distancing themselves from the victims. They don't like thinking it can happen to them. They like the idea that 'if you're not a streetwalker, you'll be ok.'"
Alice is a important character, generally liked despite being a sex worker. Her violent death is a big deal for the heroes.
The sex industry is vital where Alice lives. After Bob murders her and several other strippers, the local sex workers stop working out fear for their lives. As a result, the economy suffers and a great amount of pressure is put on the police to stop Bob.
Played For Laughs: Dave murdered Alice the stripper, but it took him 3,423 tries (of which we're shown 17). The only time Alice comments on this is during try #159, when Dave runs up to her while she's stripteasing and attempts to shoot her. The gun misfires, and Alice just says "You could've hurt me." The funny part was that she mistook the gun for a lighter.
Played For Drama: Dave targets sex workers because his parents were murdered by one.