Fellow GMs, I'm in the process of putting together some adventures for my party that are a but more investigative...

start reading as many Clue books as you can, you'll find inspiration.

No one ever means Fail of Cthulhu.
Shoegum is a marketing stunt.
But at least you got to mention it with insincere framing, again.

If you're looking to do some murder-mystery, Raymond Chandler's essay, "The Simple Art of Murder" is a must-read. He gets a bit long-winded, and he's writing about and during a very specific time of the genre, but he's spot-on about how it should all come together without leaving the audience feeling cheated.

en.utexas.edu/amlit/amlitprivate/scans/chandlerart.html

Ooh, it could mean that you found the pivotal evidence, but the pocket you placed it in has a hole in it and now you've lost it.

You find the evidence, but it looked like you tried to steal it secretly, and now everyone suspects you.

Here's how you do it

Start with a completely normal villain with a goal. But make sure that the villain's weakness is he is very easy to defeat and therefore would require sneaking through the shadows to avoid local law enforcement for whatever reason, such as a delicate political platform, or the simple fact that they are just one person.

Now, have them COMPLETE the goal, or at least complete 3/4ths of the goal, without being scene. Imagine each scene as it happens. Then imagine what is left behind in terms of clues.

Then just have everyone involved realistically lie.

Now, you may need to stretch this out a bit more if you want to make it more complicated. For instance, if the ultimate villain is someone in a position of power, ask "why would they do it themselves?" and have them hire someone else. Or pressure someone else into acting. Or pressure someone in the city watch to cover their trail. If you want to make it MORE complex, give the second in the chain a position of power to order/pressure/goad someone ELSE into doing it, etc, etc.

Remember, each person in this chain requires
1. Motive
2. Opportunity
3. Method.

Now, translating this into a game is a little bit trickier. You don't want them to just up and walk through the entire mystery piece by piece. That would be dumb. But at the same time, you don't want them to get stuck at ONE part because they failed a roll or don't know how detectives actually operate.

Instead, you lace each crime scene with at least 3 clues. One of which is always found no matter what, and the other two can be as complex as you want. Finding all 3 clues leads to a faster solution and perhaps skips a step. Finding 2 clues can lead to the correct path, but finding just that one clue is long and roundabout, maybe even leading to a red herring. This is important, because as time goes on, the criminals aren't just standing still. They know you're on the trail.

If the players are taking too long, then the criminal takes advantage of this. Another person is killed. Some evidence goes missing. The criminal manages to get further towards their escape. Something is going wrong in the ticking clock of the investigation. Remember, after about 72 hours, most crimes go unsolved after that point.

The trick is to make it all tie into the theme, and give them lots of opportunities to explore. Put lots of items at the crime scene, even if unimportant for them to investigate and determine what is necessary, and what isn't to piecing things together.

Good luck, OP.

You are overthinking this. Your method invites stalling. Instead layer your events according to the pressure they place on the party, then ramp it up as the pacing demands during play. Remain flexible. Let the players decide whom their characters trust, and let that shape the way to the finish.

I don't quite understand your critique. What part of your advice conflicts with my advice, and to follow up, aren't investigations all about stalling when you get down to it?

I meant that if you imagine a 'realistic' crime and go through the motions then the trail of clues will come out pretty random. For veteran investigators that can be a fun challenge, but it usually isn't a good idea because it makes the game boring and tedious.

You get a much more playable scenario if you go from player perspective and arrange every clue according to the natural flow of the story. Make the tension the trail of bread crumbs, not logic. Players have problems with logic. They always check the most obvious direction first. Use that to make your game good, not to make your players feel ill equipped.

Honestly, if your players have problems deducing things, I wouldn't even bother with an investigation scenario at that point. I also still fail to see where your critique really contradicts or even contrasts what I've said so far.