[TAdams8591]

I don't know what his "main" motivation was, but money was certainly a part of it. Vengeance another. Power and control another.

Whether killing was his main motivation remains to be seen. Time will tell.

[BykrBayb]

I'm sure all those were motivating factors for him. His main motivation probably changed over time. I think it started over greed, and after he enjoyed the power of killing a couple times, he became addicted to it.