Not only this, but some of the characters have a negative bias as well if they are chosen as Mr.Jack.
For Mr. Jack:
Best: Miss Stealthy. Being able to move 4 instead of 3 is a big advantage, and through buildings no less. So there a small chance of getting the Sargent to change the Cordon in Round1, and escape Round 2. A small trick the Detective should be able to stop.
Worst cases are Sherlock and the Constable. Sherlock because he's always going to get picked by the detective. And the same goes for the Constable given he is so useful to pick.
Mr.Jack is on the minority side.
As an example, take this scenario. In a game there were 4 characters left, and I as Mr.Jack was dark as was 1 other suspect (which I get to move for the last character in the round), the other 2 suspects were light.
So now I have to move towards Mr.Jack otherwise he will be the lone suspect - it's game over already. From 4 suspects.
Yes, if Mr.Jack was one of the other 2 then I would move towards the light.
But best case scenario, 1 suspect is eliminated, worst case, I lose the game.
You could suggest this is good play from my opponent, and it is, but this can happen quite frequently where Mr.Jack is on the wrong(minoirty) side and gives a HUGE deductive reasoning to narrow down suspects.
It's also easier to make people light- you simply move close to them. Keeping people dark is much harder to find corners you can't get to. So it would be better if Mr.Jack could only escape if it was light.
The best setup needs to be that an odd numbered round, Mr. Jack isn't present and you're still able to make him/her dark and close enough to escape. Ready for next round to escape. That's pretty hard thing to pull off. And the detective knowing this is your best strategy can quite easily see you trying to pull this off.