I played a long time ago, so I don't remember the case. I solved the 90% of the cases without the WT with a very stupid/effective strategy: if you can't solve it with logic, first talk to everyone at least once and select every single option, show them every evidence, ... take notes for every character and their dialogues' options and then whenever you find something new (new info, evidence, ...) repeat the dialogues. It takes time and it's stupid, but at least you'll reach the final decision --> save the game before it starts and then, again, if you didn't pay attention or you didn't notice, ... go random and if you make a mistake/lose, write down the wrong answer and load the save --> repeat until you get everything done.
I know it's a long and probably a stupid post/answer, but I don't really recall the cases since Serio stoped the updates.