People withdementia often get paranoid about people taking things. There's a reason for some of it. They feel vulnerable, especially in the stages of Alzheimer's or dementia where they remember that they can't remember. If they want to put on a sweater that is always hanging in a certain place, and it isn't there, they aren't going to remember why it's not there. If it's not there, someone must have taken it, as they certainly wouldn't have told someone they could move it or put it elsewhere. Therefore, someone stealing it is the logical conclusion.