David's right! Houdini escaped many times....Jeremy Bamber remains captured.
Don't think he needed to be Houdini, he may have been let into the house by Sheila or any other member of the family, we don't know what time he returned to WHF that night, or he may have quite simply opened the window and climbed in as he proved he could and left some other way.
You don't have to be Houdini to pull the top of a sash window right down, climb out, push it up again and climb down a ladder, I could do that without too much trouble, I'm sure.
I agree JB may have been at home in bed until the phone call from Neil woke him but if he wasn't, if he did kill the family it wasn't as hard as it can appear ay first glance for him to enter and leave after securing all windows and doors imo.