The dirty secret of every murder mystery kit is that one person has to read the answer, hand out the clues at the right moment, nudge the people who have stalled, and never get to play. Usually that person is the one who bought it. Here is how to not be that person.
Three reasons, and they are all the same reason. The clues have to be released at the right time. Someone has to keep the rounds moving. And someone has to know the solution to do either of those things. In a printed booklet, all three jobs land on one human.
A screen that knows the timing, and paper that knows the answer. Specifically:
The Conductor is a file. It does not know who you are. It does know when.
Optional characters come in pairs, so ten becomes eight cleanly. If one of the core eight is missing, the Conductor has an empty-chair switch and reads that character's testimony itself. The party does not depend on any one person, which is the whole point.
The kit includes a timeline card. One player becomes the timekeeper with a phone. The solution is sealed in the last envelope, behind the last piece of evidence, for exactly this night. You will not need it.