How could an Amalekite kill Saul? He previously killed all of the Amalekites except for King Agag who was killed by Samuel.
1:8 And he said unto me, Who art thou? And I answered him, I am an Amalekite.
1:9 He said unto me again, Stand, I pray thee, upon me, and slay me: for anguish is come upon me, because my life is yet whole in me.
1:10 So I stood upon him, and slew him, because I was sure that he could not live after that he was fallen: and I took the crown that was upon his head, and the bracelet that was on his arm, and have brought them hither unto my lord.