Well, that's the thing: there isn't any info about his circumstances or his mental state. So, we don't necessarily know what was the motive of these killings beyond financial gain.

Maybe you're right and he likes being in control and enjoys having the power to do so. Of course, normally, homeless people don't go around and kill other homeless to survive - or we just don't hear about them.

Nevertheless, He's definitely developed some mental issues and perhaps has a personality disorder. It's not a coincidence that he was sent to a mental institution.