The Cause of the Whitman Massacre

What I think caused the Whitman Massacre is the Natives thinking that Marcus Whitman losing his power to heal the sick. According to Dale A. Lambert, Marcus was healing settlers everywhere, and when the natives turned to him to help them, he couldn't. There were several other causes like the Cayuse Indians distrust for Narcissa Whitman. Also, Marcus injecting his watermelons with a disease which caused a lot of natives to be sick. But when Marcus couldn't cure them, I think, was the snapping point for the natives and they murdered 13 people including Marcus and Narcissa.