Not everything related to a quest will update your questlog... sometimes you need to do *gasp* thinking for yourself.
It's a good idea to get used to that now rather than expect heavy handholding that will never come...
Without a precision set up and specific path it's impossible to about the panties connected to the murder by normal means and conversations in the game and all of you saying that knows this. So quit acting like it's obvious and cannot be missed and if someone doesn't know you start up with the hand holding bullshit!
