Tie a rope or belt around something you consider heavy, wrap the other end around your wrist and then lean back. As long as your weight is comparable to the item you're dragging, it will move. Do the same for lifting. Put the belt or rope up over something and pull down. Using an object like a pulley immediately halves the weight you have to lift. (Plus a bit of friction) It's basic physics. There are many people over 70 that can still perform some serious physical tasks. There is no indication he was frail, underweight, sickly or bedridden. There is indication though, that he was a "rocket scientist", so creating a murder-suicide scene could have been a rather simple task for him if he put his mind to it.