1) First, fear is a motive to not commit those crimes. 2) Second, it's purpose can be to completely get rid of the evil that he or she was. If you kill the person, there's no more of his evil. Wealthy or powerful evil people can have devastating and evil effects on so many people, and so it might not be worth keeping them alive.
If you or your family have enough money (and we're not even talking about the billionaire, or even tens-of-millionaires here, but far smaller sums of cash), prison is merely a speed bump.
Locking him up would mean keeping an enemy of the state alive, an enemy with powerful friends and a very large bag of dirty laundry.
This isn't justice (this is Iran were talking about after all it's judicial system is a joke) this is spring cleaning, the sanctions have been lifted so he isn't needed anymore.