FAQ for
Where the Truth Lies (2005) More at IMDbPro »

The butler did it. Well, actually, Reuben, Lanny's assistant.

Lanny and Maureen have sex. Vince wants to join them, mainly: He wants to fuck Lanny. Lanny won't have it. In order to protect the act, Lanny tries to bribe Maureen to keep quiet, but she wants more money than he is willing to give.

Rueben was in the room all this time. He suffocates Maureen with a pillow. Her body was shipped to New Jersey in the crate with the lobsters and ice. She wasn't found in the bathtub.

Karen tells Maureen's mother her daughter was in fact murdered, but doesn't tell her who did it or his motive.

Difficult to say. Both were under the influence of drugs, and Vince more or less instructed Alice to have sexual intercourse with Karen while both were under the influence, and Alice does not technically become violent or abusive towards Karen during sex. However, despite Karen's seemingly enthusiastic response to Alice's advances, Karen is still technically drugged to the point that she no longer understands what is happening to her and what is being done to her body, so her decision is not done under her proper state of mind.