Concept:David mourned Abner’s death because Abner was treacherously killed by Joab after coming to make peace with David.
Explanation:Abner had been the commander of Saul’s army.
Earlier, during the conflict between the houses of Saul and David, Abner killed Asahel in battle at Gibeon.
Asahel was Joab’s younger brother.
Later, Abner came to Hebron to make a covenant of peace and to persuade Israel to accept David as king.
Joab was not present at that meeting.
When Joab returned and heard what had happened, he secretly sent messengers to bring Abner back to Hebron.
Joab then killed Abner to avenge the blood of his brother Asahel.
David knew nothing about this act, and when he heard the news, he wept bitterly.
David publicly mourned Abner at his grave and declared that Joab’s deed was wicked.
This shows that David considered Abner innocent and Joab guilty of the murder.
Answer:D. Joab