Mystery Cases

Hi I want to make some mystery cases that's part of a criminal organization's evil plot. But I'm having trouble making it so that it's just precisely smart enough so the local cops can't figure it out. But also flawed enough so only the genius main characters could figure it out. Any tips?

Well, the criminal organization would have to know how the cops work and tailor the plan to evade usual police procedures. Your main characters will probably look at it from a different angle since they're obviously not just gonna repeat what the cops do.

They'd probably have to know about something or someone in the organization that the cops haven't gotten to yet, but that one little thing can easily lead to a whole trail of clues.

It's important to remember that the police aren't looking for puzzles, they're looking to get their cases off the books; to a cop, unless they have concrete evidence to the contrary, their perp is whoever they can build the best case against. It might do for your villainous organization to set up some fall-guys who your hero/heroes have reason to believe are innocent. Also remember that a police force only has so many resources at their disposal, and are only likely going to be allowed to pursue a case for a finite length of time, which is no doubt something that your villainous organization could use to their advantage.

You mean like finding a good target to frame right? It's a good point.

Which reminds me I did forget to mention I thought of using preconception tricks(which are pretty much all the forms of framing) in these villain plans/mysteries too. Though I can't get too many ideas based on preconception tricks alone just yet.

One such that I thought about was set where there was a nearby forest where deep within there's an estate it's said where a vampire lives. The criminal organization creates a new murder weapon that sucks the blood out of it's victim and people will usually jump to the conclusion that the vampire did it. But the trouble was how I come up with a weapon that sucks the blood out of it's victim in a way that makes sense. So while I can piece bits of the idea together, other bits fall out of place.

preconception tricks are just one idea though right? Any other tips such as in the villains leaving none but very subtle patterns?