"Control" freaks become the most dangerous when they feel they may soon no longer hold the control over a situation.
An examination of ANS & HK$ dysfunctional relationship:
Anna, the 8th grade dropout, controlled, insulted, demeaned and treated this young male lawyer, like a piece of garbage at the beginning; taking multiple sexual partners and flaunting it in his face.
Then, as he discovered her weakness for drugs, lack of self esteem, inability to handle finances or legal stuff, he moved to reverse their roles.
I believe it was revenge that drove him to dispose of Daniel and then Anna. He may even have enjoyed describing how he overdosed Daniel - at about the time she contacted Shelley Ford - in a cry for help and a last attempt to reach out to an old, trusted friend.
Well - maybe.