Back to the Dean O'Dell mystery, my thoughts are this:
Mindy: I just can't see her hiring Keith if she actually murdered her husband. There may be something hinky going on with her (beyond the affair with Landry) but I think she's ultimately innocent of Cyrus' death.
Not!Lucky (I can never remember if his name is Tim or Ted for some reason.): We don't have a real motive, but he could have done it. Yes, the files on his computer could be season 1 Veronica, or they could be him tracking the evidence trail to make sure he didn't leave any leads back to him. He also had access to Veronica's perfect murder paper (if it wasn't posted, in which case everyone has access.)
Landry: Maybe. He's got motive, sort of. But I don't see him really thinking of Cyrus as someone who needed to be bumped off. However, he could have taken Mindy's car back to the college to off O'Dell and that's how it ended up being egged.
Right now, my prime candidate is the teenage son. He had motive, he's stolen O'Dell's car in the past (which would explain how the car got egged), I can definitely see O'Dell's reaction to showing up at his office at 2am to be "What are you doing here?" whereas Mindy or Landry would probably get a more visceral reaction, considering his mental space at the time, and he certainly doesn't seem to be shook up by the whole ordeal. I can also see a teenager downloading instructions on how to commit a perfect murder from the internet (if Veronica's paper was indeed posted) and following them to the letter.