New thought, and this is based on speculation completely as I don't know where the LoVe relationship is going after ep 21. What if the murderer is Aaron (or Lynn) and Veronica exposes this; this in turn sends Logan reeling away from her, feeling betrayed all over again. He leaves for the summer and the next season begins with Veronica on the outskirts for locking away the famous Aaron or beating a dead horse (dead Lynn -- if she's even dead) and she sees Logan for the first time since they broke up. He's at the table with the 09ers and Dick Casablancas or one of them makes some snide comment about Veronica and Logan tells them to shut up, back off, whatever. While Duncan sits and says nothing. Wouldn't it be interesting if Logan then kinda turned on Duncan with a "how the hell could you sit by all year last year and let her be tormented by everyone and not do anything?"
I think we all know that with one word, Duncan definitely could have stopped Logan (see the Pilot when we do see Duncan -- one time -- tell Logan to stop and Logan does) and everyone seems so in awe of Duncan, I think it would have turned into just ignoring her more than anything.
I just think it would be an incredibly cool play, should Veronica and Logan be on the outs with Veronica the "betrayer" again, if Logan -- unlike Duncan -- shuts other people down for turning on her so viciously. And we see Logan confront Duncan about it. I've always felt that as horrible as Logan's early treatment of Veronica was, Duncan's was in a way worse. He just stood idly by and let them all do it.