How we cite our quotes:
Quote #4
But Absalom sent secret messengers throughout all the tribes of Israel, saying, "As soon as you hear the sound of the trumpet, then shout: Absalom has become king at Hebron!" Two hundred men from Jerusalem went with Absalom; they were invited guests, and they went in their innocence, knowing nothing of the matter. While Absalom was offering the sacrifices, he sent for Ahithophel the Gilonite, David's counselor, from his city Giloh. The conspiracy grew in strength, and the people with Absalom kept increasing. (2 Samuel 15:10-12, NRSV)
But Absalom sent spies throughout all the tribes of Israel, saying, As soon as ye hear the sound of the trumpet, then ye shall say, Absalom reigneth in Hebron. And with Absalom went two hundred men out of Jerusalem, that were called; and they went in their simplicity, and they knew not any thing. And Absalom sent for Ahithophel the Gilonite, David's counsellor, from his city, even from Giloh, while he offered sacrifices. And the conspiracy was strong; for the people increased continually with Absalom. (2 Samuel 15:10-12, NRSV)
We don't fully know why Absalom does this, but we're left to assume that his complicated family history with David, in addition to the fact that he's promised the people a more just kingship, all plays into it.
Quote #5
Ahithophel said to Absalom, "Go in to your father's concubines, the ones he has left to look after the house; and all Israel will hear that you have made yourself odious to your father, and the hands of all who are with you will be strengthened." So they pitched a tent for Absalom upon the roof; and Absalom went in to his father's concubines in the sight of all Israel. Now in those days the counsel that Ahithophel gave was as if one consulted the oracle of God; so all the counsel of Ahithophel was esteemed, both by David and by Absalom. (2 Samuel 16:21-23, NRSV)
And Ahithophel said unto Absalom, Go in unto thy father's concubines, which he hath left to keep the house; and all Israel shall hear that thou art abhorred of thy father: then shall the hands of all that are with thee be strong. So they spread Absalom a tent upon the top of the house; and Absalom went in unto his father's concubines in the sight of all Israel. And the counsel of Ahithophel, which he counselled in those days, was as if a man had enquired at the oracle of God: so was all the counsel of Ahithophel both with David and with Absalom. (2 Samuel 16:21-23, KJV)
This is the moment when Absalom can't turn back. When he has sex with his father's concubines—publicly, it seems—he's seized too much power for it to be reversible (although David still wants to forgive him, or, at least, not kill him).
Quote #6
When Ahithophel saw that his counsel was not followed, he saddled his donkey and went off home to his own city. He set his house in order, and hanged himself; he died and was buried in the tomb of his father. (2 Samuel 17:23, NRSV)
And when Ahithophel saw that his counsel was not followed, he saddled his ass, and arose, and gat him home to his house, to his city, and put his household in order, and hanged himself, and died, and was buried in the sepulchre of his father. (2 Samuel 17:23, KJV)
We're supposed to assume that Ahithophel deserves this for betraying David. From Christian perspectives, he appears to be a forerunner of Judas Iscariot and his betrayal of Christ.