my mom used to work with children with autism, and i volunteer with them presently, and i know how sometimes they can get fixated on the strangest things. this actually isnt the first serial killer loving kid i have met, theres absolutely nothing wrong with the boy, he doesnt need therapy, thats just how kids with autism can be sometimes, they latch on to one thing, usually something having to do with problem solving and how other people think, since they have problems connecting to others, they like to see why people do strange things, like kill people, and learn a lot about it so they can understand. what i did for the boy that i know who had a killer interest, i instead turned him on to the forensic scientists who catch the killers, and taught him about killer phycology, and criminal profiling, some say he wont understand things like that, but hes a very smart boy and it sounds like your coworkers son is smart as well. now hes constantly asking me to set up crime scenes for him to solve. what you could do is set up a forensic catch the killer party, like the one you were describing. but you have to make it child friendly so you wont upset the childrens parents, i understand you want to make it fun for him, but most kids wouldnt be interested in the night stalker and can get scared and their parents dont want them hearing about that kind of thing. they may even be uncomfortable about there being killing involved, at such a young age, most people dont understand children with autism can be very mature and fascinated by these things and think what the other people you asked thought, that he needs help, and wont let their children come and you dont want that. what i suggest is you set up a crime scene, instead of a real person, make the victim someone they would connect with, the boys favorite cartoon character, and instead of him getting murdered, have them get something stolen, then set up different stations that they go to to solve the crime, break them up into teams . at the first station, pretend to be a witness and describe the criminal so they can make criminal sketches, then at the next station, you can get synthetic blood that they can test blood types on, then at the next station they can compare footprints found at the scene with those of the suspects, and so on and so forth. then at the end they all guess who the criminal is, and whichever teams get it right get cardboard forensic scientist badges. then you can have someone play the criminal and they get to arrest him. this way he gets his crime scene fun while keeping it appropriate for the other kids. you can make a cake with a body outline on it, like this one they made for CSI, only without CSI written on it:

http://www.csifanatic.com/files/2009/02/zumawirewe...

for a present you could give him a book on serial killers or suggest it to your coworker for him to get heres a good one:

http://www.amazon.com/Killer-Book-Serial-Killers-I...