I believe it's Henry because he has alot of reasons to kill some of the people that have been killed. Like Mr. & Mrs. Wellington and Richard Allen. Richard said (I think he did at least) that Henry would never be a Wellington, the father hated him, and I'm not sure about the step-mom. As for J.D. and Uncle Marty. Uncle Marty could have known Henry was the killer and was gonna black mail him, you know like use it against him. As for J.D. he could have been getting close to telling everyone Henry's secret. As for Malcolm, Lucy, and Beth...I dont know. But this is just my theory.