“The player will always know who’s the traitor” – how do you expect that you’ll know?
What if your investigations never lead to either a confession or a smoking gun? What if it remains hard in the game (as in life) to distinguish coincidence from conspiracy?
What if the consequences of eliminating possible traitors early are ambiguous and hard to interpret, and require several playthroughs to weigh up against each other?
What if even a betrayal that leads to your death and the eradication of your rebellion doesn’t leave the reader entirely clear on who betrayed you?
The identity of the Rim Square traitor is not and will definitely not be random. That’s not the kind of story I’m interested in telling here. But when all’s said and done, there should be enough ambiguity to get players through several playthroughs before they’re confident in their interpretation of the evidence.