I need to throw a serial killer themed party for children?

My co-worker has a son who is turning seven soon and asked me to help plan the party. His mother died when he was a baby and he's never had a birthday party. He also has mild autism and fixates on certain subjects. His latest obsession happens to be serial killers - he reads books about them all the time and... show more My co-worker has a son who is turning seven soon and asked me to help plan the party. His mother died when he was a baby and he's never had a birthday party. He also has mild autism and fixates on certain subjects. His latest obsession happens to be serial killers - he reads books about them all the time and talks about them constantly. He says he wants his party them to be serial killers and his favorite is Richard Ramirez. How can I incorporate this theme without upsetting the other parents? I'm thinking about maybe a spin on "murder mystery" parties where the mystery can be based on real killers.

I also inquired about this in entertaining but wasn't getting very good answers; they just keep telling me this child needs therapy which is very offensive because of course, he is getting treatment for his autistic disorder and no one thinks his serial killer interest is a problem. I hope that parents might be more understanding?
Update: There will be about five or six other kids attending, ages 7-10. Two are his cousins and the rest will be from his class at school. His schoolmates are all pretty advanced in intelligence because he has skipped a grade but he has a hard time with regular socializing so I need activities to keep them engaged together.
Update 2: Well considering these kids talk to him every day I imagine he's probably already told them all about this subject so it's not like it's their first hearing of serial killers. And he's in the advanced second grade class and his reading class is with third graders. The cousins are in 3rd and 4th.
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