In God's last killing, he sent a lion to kill a man for not smiting a prophet when the prophet asked him to. But the next guy that came along was willing to do it, so the prophet was able to put ashes on his face and have a proper disguise for his meeting with King Ahab.
When King Ahab passed by, the prophet (with his cool disguise) said to him:
Thy servant went out into the midst of the battle; and, behold, a man turned aside, and brought a man unto me, and said, Keep this man: if by any means he be missing, then shall thy life be for his life, or else thou shalt pay a talent of silver. And as thy servant was busy here and there, he was gone. 20:39-40a
Which, of course, was complete bullshit. God's prophet was not only crazy, but a liar, as well.
King Ahab played along, though, and said, "OK, whatever."
The king of Israel said unto him, So shall thy judgment be; thyself hast decided it. 20:40b
Then the prophet wiped off the ashes on his face and revealed his true identity. He was a prophet! (It's really hard to tell a prophet when he has ashes on his face.)
He ... took the ashes away from his face; and the king of Israel discerned him that he was of the prophets. 20:41
And then the prophet told King Ahab the bad news. God was going to kill the king (and his family, of course) for letting king Benhadad live. (See 1 Kings 20:34)
hus saith the LORD, Because thou hast let go out of thy hand a man whom I appointed to utter destruction, therefore thy life shall go for his life, and thy people for his people. 20:42
And that's what happened. God carefully arranged things so that King Ahab would die while fighting the Syrians.
The battle increased that day: and the king [Ahab] was stayed up in his chariot against the Syrians, and died at even: and the blood ran out of the wound into the midst of the chariot. 20:35
And that is God's last killing in 1 Kings 20. (Five in one chapter!)