There is the law of selfpreservation written by God himself on our hearts.

There is the primal compact and bond of society, not graven on stone, or sealed with wax, nor put down on parchment, nor set forth in any express form of words by men when of old they came together; but implied in the very act that they so came together, pre-supposed in all subsequent law, not to be repealed by any authority, nor invalidated by being omitted in any code; inasmuch as from thence are all codes and all authority.
"Neither do I well see wherefore you cavaliers, and, indeed, many of us whom you merrily call Roundheads, distinguish between those who fought against King Charles, and specially after the second commission given to Sir Thomas Fairfax, and those who condemned him to death.

Sure, if his person were inviolable, it was as wicked to lift the sword against it at Naseby as the axe at Whitehall.

If his life might justly be taken, why not in course of trial as well as by right of war?
"Thus much in general as touching the right.

But, for the execution of King Charles in particular, I will not now undertake to defend it.