What if the girl knew the guy was a serial killer and that's why she wanted him on her show? It is a webcam so there is the illusion of safety there and the girl was trying to get a show full of serial killers and interview them.
Maybe she was doing the show as ploy to find out how serial killers work and then she becomes the serial killer of serial killers and comes after these guys. A little role-reversal.
Just trying to come up with a fresh idea here :)
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