Ah my bad. I assumed you, the GM, knew the answer to the mystery. Like you had a specific person in mind before the investigation happened.
That was what I did with my previous, "Jinnistani eclipse-celebration masquerade ball" mystery. I had a specific person in mind and chose clues to place for the PCs to figure it out. A mixture of intentionally false clues and real ones. The killer (technically it could be classified as an assassination) did the killing specifically to cause unrest in the court of this particular Jinnistani city-state. Mt. Matahat. She wanted to try to frame at least one hot-headed visiting nobleman (The Right Honorable Afzal Hasan Anwar al-Aqil yatt-Mejjati, Baron of Cinders) in order to disrupt trade between Mt. Matahat and the City of Brass, probably with an eye toward setting up someone else for a better position in the never-ending squabbles over who gets to rule there.*
I have, however, resolved to do something
like the Clue/Cluedo method for my game at some point in the future. Al-Rakkah Confidential, hah. I think my group would appreciate some good ol-fashioned sleuthing. By keepng the true solution secret even from myself, I can potentially do something very interesting!
Given the PCs got Baron Afzal off the hook back in Mt. Matahat, he might even intentionally hire them as private investigators, knowing they are trustworthy and willing to follow the truth, and (best of all) highly unlikely to accept bribes or other such interference. Could be a good idea, if the party ever decides to hit up the City of Brass...
*Unlike most Jinnistani city-states, the City of Brass has no single ruler, as the former Inferno Queen died, very unexpectedly since Jinnistani nobles are usually nigh-immortal, without having designated a specific heir amongst her many,
many children...and they've never been able to completely settle behind a single ruler. The throne has lain vacant for over a thousand years because anytime someone gets close, it pisses off enough other pretenders to take them down. Sort of an "if I can't have it, no one can" situation.