How we cite our quotes:
Quote #1
David said to the young man who had reported to him, "Where do you come from?" He answered, "I am the son of a resident alien, an Amalekite." David said to him, "Were you not afraid to lift your hand to destroy the Lord's anointed?" Then David called one of the young men and said, "Come here and strike him down." So he struck him down and he died. David said to him, "Your blood be on your head; for your own mouth has testified against you, saying, 'I have killed the Lord's anointed.'" (2 Samuel 1:13-16, NRSV)
And David said unto the young man that told him, Whence art thou? And he answered, I am the son of a stranger, an Amalekite. And David said unto him, How wast thou not afraid to stretch forth thine hand to destroy the Lord's anointed? And David called one of the young men, and said, Go near, and fall upon him. And he smote him that he died. And David said unto him, Thy blood be upon thy head; for thy mouth hath testified against thee, saying, I have slain the Lord's anointed. (2 Samuel 1:13-16, KJV)
David repays the Amalekite for helping Saul commit assisted suicide with, well, more death… even though David almost fought against Saul's army on the side of the Philistines.
Quote #2
Afterward, when David heard of it, he said, "I and my kingdom are forever guiltless before the Lord for the blood of Abner son of Ner. May the guilt fall on the head of Joab, and on all his father's house; and may the house of Joab never be without one who has a discharge, or who is leprous, or who holds a spindle, or who falls by the sword, or who lacks food!" (2 Samuel 3:28-29, NRSV)
And afterward when David heard it, he said, I and my kingdom are guiltless before the Lord for ever from the blood of Abner the son of Ner: Let it rest on the head of Joab, and on all his father's house; and let there not fail from the house of Joab one that hath an issue, or that is a leper, or that leaneth on a staff, or that falleth on the sword, or that lacketh bread. (2 Samuel 3:28-29, KJV)
Again, a cynical reader might read this as a moment of protesting a little too much on the part of the narrator. The narrators insist so strongly that David had nothing to do with Abner's death that you might start wondering if David did have something to do with Abner's death.
Quote #3
David answered Rechab and his brother Baanah, the sons of Rimmon the Beerothite, "As the Lord lives, who has redeemed my life out of every adversity, when the one who told me, 'See, Saul is dead,' thought he was bringing good news, I seized him and killed him at Ziklag—this was the reward I gave him for his news. How much more then, when wicked men have killed a righteous man on his bed in his own house! And now shall I not require his blood at your hand, and destroy you from the earth?" So David commanded the young men, and they killed them; they cut off their hands and feet, and hung their bodies beside the pool at Hebron. But the head of Ishbaal they took and buried in the tomb of Abner at Hebron. (2 Samuel 4:9-12, NRSV)
And David answered Rechab and Baanah his brother, the sons of Rimmon the Beerothite, and said unto them, As the Lord liveth, who hath redeemed my soul out of all adversity, when one told me, saying, Behold, Saul is dead, thinking to have brought good tidings, I took hold of him, and slew him in Ziklag, who thought that I would have given him a reward for his tidings: how much more, when wicked men have slain a righteous person in his own house upon his bed? shall I not therefore now require his blood of your hand, and take you away from the earth? And David commanded his young men, and they slew them, and cut off their hands and their feet, and hanged them up over the pool in Hebron. But they took the head of Ishbosheth, and buried it in the sepulchre of Abner in Hebron. (2 Samuel 4:9-12, KJV)
This is a little similar to the Amalekite killing earlier in the text. David is willing to fight against Saul's family's army but not to actually kill any of Saul's family members (except when he lets the Gibeonites sacrifice some). It's a subtle distinction.