Atonement: how to take away the wrath of God

In the days of David they were short of food for three years, year after year; and David went before the Lord for directions. And the Lord said, On Saul and on his family there is blood, because he put the Gibeonites to death.
2 Samuel 21:1

So David said to the Gibeonites, What may I do for you? how am I to make up to you for your wrongs, so that you may give a blessing to the heritage of the Lord?
2 Samuel 21:3

Traitors to the King

Now by chance there was present a good-for-nothing person named Sheba, the son of Bichri, a Benjamite: and he, sounding the horn, said, We have no part in David, or any interest in the son of Jesse: let every man go to his tent, O Israel.
2 Samuel 20:1