Why did the cayuse murder the Whitman and?

The Cayuse Tribe killed Dr. Whitman because he is the reason settlers, also known as the whites, came to Walla Walla Washington. This angered the Cayuse Indians. The whites had brought measles with them and unfortunately they started to spread and the Cayuse got measles. Dr. Whitman was the shaman which means it's his duty to restore their health. Many Cayuse died of measles but the whites got well. The Cayuse lacked immunity so this is why it was hard to restore their health. Joe Lewis, a white settler, wanted to take over Dr. Whitman's place as shaman so he spread rumors to the Cayuse that Marcus was poisoning the Cayuse and since Dr. Whitman was white, he was helping the whites. The Cayuse Tribe believed this and killed Dr. Whitman in his own home. 13 or 72 people were killed during the Massacre.