Fourfold Restitution
“If a man shall steal an ox, or a sheep, and kill it, or sell it; he shall restore five oxen for an ox, and four sheep for a sheep.” (Ex. 22:1)
“And he shall restore the lamb fourfold, because he did this thing, and because he had no pity.” (2 Sam. 12:6)
Since Nathan’s parable in 2 Sam. 12:1-4 likened Uriah to a lamb: David paid four deaths for Uriah’s death.
All of this took place before the Book of II Samuel ends.