Thematic Bible: David's other deceits with the philistines

Then David and his men went up and raided the Geshurites, the Girzites, and the Amalekites. (They had been living in that land for a long time, from the approach to Shur as far as the land of Egypt.) When David would attack a district, he would leave neither man nor woman alive. He would take sheep, cattle, donkeys, camels, and clothing and would then go back to Achish. When Achish would ask, "Where did you raid today?" David would say, "The Negev of Judah" or "The Negev of Jeharmeel" or "The Negev of the Kenites." read more.
Neither man nor woman would David leave alive so as to bring them back to Gath. He was thinking, "This way they can't tell on us, saying, 'This is what David did.'" Such was his practice the entire time that he lived in the country of the Philistines. So Achish trusted David, thinking to himself, "He is really hated among his own people in Israel! From now on he will be my servant."