You shouldn't call him a bastard. There was something clearly wrong with him. If he was selling your stuff off to support a Viagra habit so he could bone your mom, that would be a bastard. Hoarding your stuff means he had some kind of weird attachment to you.

He had been stealing from her since the day she moved in, over nine years. I think bastard is a fairly light term for this unless there is some revelation of other mental health issues. We can't just assume he had them because he did weird stuff. He may have, and that may explain it, but telling OP not to assume he didn't is the same as me telling you not to assume he did. Neither of us know.