What gave Henry motive to kill Thomas Beckett?

Actually, King Henry II did not order the execution or assassination of Thomas a' Beckett. Henry was known to have a horrible temper, and in haste shouted aloud in the presence of his knights "Who will rid me of this troublesome Priest". Four of King Henry II's Knights took his Words to mean he wanted Thomas killed; he actually did not literally want anyone to kill Thomas. ---- he didnt agree about the pope