Wild Things: Diamonds in the Rough

Set, like the previous films, in the fictional south Florida port town of Blue Bay, 18-year-old spoiled rich girl Marie Clifton (Sarah Laine) is set to inherit two beautiful diamonds, called the "mother and daughter". Marie's stepfather, Jay Clifton (Brad Johnson), challenges the will claiming that he believes Marie is not ready for the responsibility, but actually wishing to claim the diamonds for himself. At a sexual education seminar, physician Chad and probation officer Kristen Richards (Dina Meyer) discuss sex crimes. Kristen Richards reveals that she was a victim of an anonymous rapist many years before.At Marie's swim-meet, Jay encounters Elena Sandoval (Sandra McCoy), an unpopular poor girl from her school and invites her to a party he planned for Marie. She attends, and Marie, upon seeing her, fights with her and throws her into the pool. Later, Elena encounters Jay. The audience does not see what happens next, and the next thing it learns is that Elena accuses him of raping her. Chad investigates and testifies to the court that he believes Elena was raped.Marie believes that Elena is doing this for money and tells Jay to "find her price" and pay her. Jay admits that he's broke and Marie suggests that they sell the diamonds. Jay agrees. Later, Elena goes to Marie's house, where she meets Marie and Chad, and the three of them make love in a threesome... having all been working together to get Jay to give up the diamonds.The next day, in court, Elena says that Jay didn't just rape her but also threatened to kill her if she told anyone. However, Kristen now believes Elena is lying (Elena uses something Kristen's rapist told Kristen the night he raped her: "You won't remember, but you'll never forget.") Kristen tells this to Detective Michael Morrison (played by Lynden Ashby, reprising his role from the previous movie, Wild Things 2), who agrees to look into it. Kirsten and Morrison search Elena's trailer and find she has been gathering information about Kristen's "rape".However, Chad begins acting nervous and gets Marie to let him see the diamonds before drugging her and stealing them. The two girls chase him into the woods, where Marie finally catches him and kills him with a tire iron. Marie goes to meet the buyer that Chad set up and learns that the diamonds are fake, while Elena stays in the woods, where she is caught by Kristen (who is also her probation officer) and Detective Morrison.Kristen and Morrison offer Elena a deal as well as a dangerous task: get Marie to admit she killed Chad, and the fraud charges against Elena will be lessened. However, Elena is unsuccessful. The girls go to get the diamonds (with and the detective listening via wire), and Elena pulls a gun and flees with the diamonds. Kristen goes in and shoots Marie in the chest, killing her.At the end of the film, it is revealed that BOTH Kristen and Elena are actually mother and daughter and that Jay was the man that raped Richards in 1988 and that Elena is the daughter... born of that rape.During the credits, scenes are shown explaining how they managed to pull all of this off, and Kristen and Elena are together enjoying their two new inherited diamonds, while the again-duped Detective Morrison is left all by himself to ponder being fooled by another femme fatal for the second time.

Question: Who killed Chad?
Answer: Marie