I saw this case on Solved this morning.
https://en.wikipedia.org/wiki/Murder_of_Brian_Stidham
I think it illustrates why the "hit man" theory in regards to Dan's case is such a dicey one. You'll notice how quickly the shooter and the planner got caught. And this was a shooting that was planned out. I think it also caught my attention because it took place among the "educated" part of our society. A Dr. wanting another Dr. dead. In Dan's case, a lawyer being murdered, with the suspicion that his lawyer ex wife had something to do with it.
We have to remember that most people are amateurs when it comes to killing someone else. Even in this Stidham case, the shooter was a career criminal. Still, that made no difference--he got caught.
When bringing another person into a crime, the variables don't double. They actually go up exponentially. Thus, the chances of getting caught go up exponentially. In other words, there's a reason there aren't many "tag team" serial killers in history.
This is the exact reason I continue to believe Dan's murder was a solo effort. If this had been a conspiracy against Dan by someone close to him, the police would've figured it out by now just like they did in the Stidham case.