Who betrayed the Nee-Me-Poo causing Chief Joseph to proclaim “all tribes are enemies”?

The Crow tribe betrayed the Ne-mee-poo, causing Chief Joseph to proclaim “Now all the tribes are enemies”.

From the text:

At last we arrived at a Crow camp. The braves ate with us. They smoked long-stemmed ironwood pipes with the face of their chieftain carved on the bowls and treated us as friends. They gave us bullets. But in the end, fearing the revenge that the White Soldiers might put on them, they refused to help us.