2 Samuel 3:23-27

When Joab and all the army that was with him arrived, they informed Joab, saying, “Abner the son of Ner came to the king, and he has let him go on his way, and he has gone in peace.”

Then Joab came to the king and said, “What have you done? Behold, Abner came to you; why then have you let him go, so that he is already gone?

You know Abner the son of Ner, that he came to gain your confidence, and to learn of your going out and coming in and to find out everything that you are doing.” Joab Murders Abner

When Joab left David’s presence, he sent messengers after Abner, and they brought him back from the well of Sirah; but David did not know about it.

So when Abner returned to Hebron, Joab took him aside into the middle of the gate to speak with him privately, and there he struck him in the belly, so that he died on account of the blood of his brother Asahel.