The truth of the matter is that the actually art of catching and convicting criminals is an incredibly complex process. There's literally no TV show or Movie that comes even close to how it works. It's systematic, tedious, and incredibly bureaucratic.
So really it's a matter of making it truthful (and boring) or complete bull (and enjoyable).
Or... Leave the authorities out altogether.
Sure it's a bit cliche, but your typical "There's been a murder, and it was one of us" stories are usually pretty good. Make the catching of the murderer essential to the plot resolution, and you have a story. Say the characters are on a boat. A piece of the engine goes missing, and an engineer is killed. Slowly others start dropping like flies as well. Find the murderer, retrieve the engine piece, get home safely.
Same template could be repeated several ways: Old mansion with only one broken phone link to the outside world, for example.
Also, I have a possible resolution to this problem:
Outside of the mystery itself, there'd be little room for players to make their own lore or story input, it'd mostly be character development which isn't bad, but I liked the kind of world we'd all created for WoA.
Encourage RPers, or demand it if you feel evil enough
, to create mysteries within the main mystery.
The owner of the boat, for example, has gone broke, and would make a fortune off of the insurance.
One of the engineers is an illegal immigrant, and the other engineer had just found this out.
Shady business deals, affairs, armed robbery.
Let players reveal clues to their own story at their own discretion, allowing input, and throwing everyone else off the scent of the main story.
Possible suggestions for consideration