Murder, you wrote

Ever thought of writing your own murder mystery script for a party? Halloween is still almost a month away, so there’s time. Or it could be an unusual birthday party idea. Try this site for help on the “how to”s.

Of course, you can buy mystery party materials. This site looked interesting.
And this one was especially aimed at kids.

Here’s a helpful article: “Host a Murder Mystery Party for Your Tween or Teen.”

And I know you can also buy mystery jigsaw puzzles. You put the puzzle together to solve the mystery story that comes with the puzzle. If you can’t find them at local toy store or bookstore, try this site.

This fill-in invitation might work for a mystery party.