For David had said to the Amalekite, “Your blood be on your own head because your own mouth has testified against you, saying, ‘I killed the LORD’s anointed.’”
Here is, I. David's reception of these tidings. So far was he from falling into a transport of joy, as the Amalekite expected, that he fell into a passion of weeping, rent his clothes (Sa2 1:11), mourned and fasted (Sa2 1:12), not only for his people Israel and Jonathan his friend but for Saul his enemy.
Commenting on 2 Samuel 1:11-16
And David said unto him, thy blood be upon thy head,.... The blood that he had shed, let him suffer for it; for as he had shed blood, his blood ought to be shed, according to the law of God; and for proof of this, that he had so done, he appeals to his own confession: for thy mouth hath testified against thee, saying, I...
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. (f) You are justly punished for your fault.