What makes him a sociopath?

If you are willing to consider murdering your business competition, you are probably a sociopath.

Actually, considering something has nothing to do with being a sociopath. Neither does doing something. A lack of conscience is a hallmark of a sociopath. Killing someone does not make you a sociopath. Showing no signs of conscience over the killing points toward you being a sociopath.

He was sentenced to the maximum for consistently showing no remorse for any of his actions. Thus, sociopath.

He doesn't seem like a sociopath. More like a power-hungry narcissist. He expressed regret and hesitation multiple times over (what he thought were) the murders, but simply insisted "it had to be done".

Not to detract from your point. I think he deserves life without parole for the attempted hits by themselves, ignoring every other charge. (Despite the fact that's not what he was convicted of.)