Comments on each level:
Case 1: Last Stop Spoilers
Nice and straightforward. Only one suspect can possibly visit the scene.
STATUS: SOLVED
Case 2: The Science of Deduction Spoilers
Thanks to help from the author. All 3 suspects visit the scene, so the additional rules come into play. The murderer kills the victim on first contact at the scene and no innocent suspect enters the room with a dead body. This means…
Look for the suspect whose first contact happens after everyone else has passed through the scene for the last time.
STATUS: SOLVED
Case 3: Foreclosure Spoilers
Only one suspect’s path passes through the vault.
STATUS: SOLVED
Case 4: Exit, Pursued by a Bear Spoilers
Things are getting trickier. I won’t know if a suspect truly visits the scene if they enter one of the adjacent rooms.
Still working through this one to understand why I got it wrong.
STATUS: UNSOLVED
Case 5: Smoke and Mirrors Spoilers
There are multiple permutations which makes things interesting.
One potential combination allows O.O. to first visit the scene at 19:15, with the others not visiting after, so I’m surprised that O.O. was not the correct answer.
Seeing the right answer, I notice that M.M. sees a witness on first visit to the scene (N.N.) Therefore, they must do the job on a later visit.
STATUS: UNSOLVED
Case 6: Aftertaste Spoilers
The cause of death is unique in this one! No suspect visits the crime scene, so they must have planted the poison before Y.Y. visits the bathroom at 20:00. All actions taken after 20:00 can be discarded, making things a lot simpler. Did anyone visit a room before Y.Y. reached it? Yes, in fact - just one.
STATUS: SOLVED
Case 7: Occam's Razor Spoilers
Potential issue: Z.Z.‘s path doesn’t lead them to the crime scene. (Library is blocked by X doors and Z.Z. has no X)
Potential issue: T.T. doesn’t appear to have any valid path. (Stuck at ~23:35 in Aquarium)
STATUS: UNSOLVED