|Complete Bright Lights, Flying City||16||Marshall Friedman (Sanctuary)||1305 XP, Pistol|
It seems that Justin MacReady has been murdered and Marshall Friedman needs your help in determining the culprit. You only need to identify the killer to finish the mission, with optional objectives to question the Marshall himself, Moxxi and Dr. Zed. Since these are very easy optional objectives, it's a good idea to do them to have them count towards the Compl33tionist challenge.
Each of the three people you talk to will provide a clue as to who the real culprit is. Friedman says it was a single shot, while Zed says he healed him completely. Moxxi mentions that she put a couple of bullets into him and damaged his shield (shields will regenerate). Using that knowledge, you can deduce that the one with the sniper rifle is the true culprit, so accuse him. If you guess the wrong one, the true guy will run away and you will still pass the mission.