John Gill Commentary 1 Kings 20:40

"And as thy servant was busy here and there, he was gone. And the king of Israel said unto him, So shall thy judgment be; thyself hast decided it." — 1 Kings 20:40 (ASV)

And as your servant was busy here and there, he was gone
Employed in one thing or another relative to the battle, his prisoner committed to his care made his escape:

and the king of Israel said to him, so shall your judgment be, you yourself
have decided it ;
the sentence was plain and open against him, that either he must die or pay the money, for he himself had agreed to it.