Originally Posted by MissMonkeyMoo:
“I've always believed that Bobby does know what he did to Lucy. It's ridiculous that a) he hit her over the head then couldn't wake her up but thinks she died due to someone elses actions b) never said to Ian or Peter that he was dad that the last time he saw Lucy they argued and he hit her. I know Jane is supposed to have told him to keep that a secret but a ten year old boy would say something about it unless he knew he was responsible. He is definitely that manipulative - look at the way he got Jane to get him the bike! And he is always lurking around corners listening to conversations.”
I think he has known all along too, hence him behaving however he wants and hurting whoever he feels has wronged him in someway. I mean, his mother covered up the fact that he had killed his sister, if you knew that you'd feel pretty invincible.
I believe he hurt Dennis because he was afraid Dennis would spill the beans about him being Lucy's killer to other people and Jane had covered up for him once, he probably thought if he killed Dennis that she would cover for him again or take the fall for him anyway.
I'm also not convinced that Lucy's death was an accident to be honest. I think Bobby was angry that Lucy was getting a lot of attention at the time and the family was fracturing due to her antics, with her out of the way he probably had this vision of a peaceful family life and he'd be the centre of attention. He is one messed up kid.