Any chance WM was doing the "tough love" bit with DM, wanting him to grow up? I have to wonder if DM was having a hard time living on the amount of "salary" WM was giving him. Maybe more responsibility was being thrusted on DM, or he was being made to be accountable? Especially if DM was acting disinterested in the business. I don't think everything was roses in the M/B household(s) when it came to DM. I still think the incinerator was ear-marked for WM, and DM couldn't go through with it after the (alleged) murder.
I really think the WM murder had all to do with a kid not wanting to grow up, and a father paying the ultimate price when poo hit the fan. DM was spoiled, entitled and bitter. I wonder how much time he spent gaming, and if WM wanted him to start to pull a bit more weight and act/get involved in the business more. After all the money was spent, basically for DM's future and the future of MillardAir, as a parent, I certainly would be pissed if I thought my kid was still acting like he was 19.
What I really want to know is if there was a "cut-off" date. On such and such a date, your "salary" will be cut to this if you don't shape up. Was WM co-signer on any of the properties for DM? Was he paying the expenses? Etc etc etc
This is TB's murder, but it goes to the entitlement mindedness of DM. What he wants, he's going to take.