Commentary for Genesis 20:10

ויאמר אבימלך. Avimelech said. Seeing that the previous verse had been a rebuke only, he now switched to a question. This is why the sentence had to begin once more with the words: "Avimelech said," though Abraham had not yet responded to the accusation. Avimelech now conceded that he did not consider Abraham capable of wanting to harm him intentionally.

ויאמר, Avimelech wanted to know why Avraham had not personally protested the forced abduction of Sarah instead of allowing the king to become guilty of a greater crime. Surely a man such as he must have had a good reason for allowing this to happen without protest!?

What did you see. What caused you to fear me? — The Philistines of those days were civilized and honorable.