The man who first saw Absalom hanging did not kill him because he was

When Absalom rebelled against his father David, a battle ensued between Absalom's army and David's army. During the battle, Absalom was riding his mule through the forest when his head got caught in a tree. He was left hanging in mid-air, unable to free himself. The man who first saw him was Joab, the commander-in-chief of David's army. However, Joab did not kill Absalom, but instead informed David about Absalom's fate. It is not explicitly stated why Joab did not kill Absalom, but one possible reason is that he knew that David did not want his son killed, even though Absalom was rebelling against him.