My opinion is that when Pierce Marshall died on June 20, 2006 HKS decided it was the perfect time for him to take over the lawsuit 100%. He may have figured the competition was now gone or weak and ANS and Daniel would just get in his way and he'd have to split the proceeds should he win the lawsuit in CA. ANS being pregnant and leaving him the guardian of the child would make things easier and would be like icing on the cake.
I think the death at the Hard Rock was an accident. They needed to keep her alive just one more day.
It would have been much easier to drop her overboard on the way back to Nassau. No body = no questions.