'A just punishment'? These are your words, not Jesus'. 

He was clear to those who tried to test him over the woman caught in adultery. He didn't tell the unmerciful mob that the punishment they sought was not just. No; instead he set the ground for exercising it: sinlessness.

Are you sinless? Is the State? If you both are, then go ahead and execute till your righteous hearts' content. But if you aren't and, yet, proceed, then you are liable to harsh judgement.

You know Jesus' words. You have no excuse.

You are either for him, or against him.

It's your call.