WHY, Ariz.—Yvonne Nevarez remembers her late uncle Raymond Mattia as a proud Tohono O’odham Nation member who always took a stand against injustice. He was a kind, respectful, peace-loving man, she said, making his shooting death by U.S. Customs and Border Protection (CBP) agents even harder to accept. “I’m angry. I can’t believe it. I…