PHOENIX (AP) — A man charged in the disappearance of a Navajo grandmother whose case has highlighted the crisis of violence against Native Americans pleaded guilty Thursday to robbery as part of a second agreement reached with prosecutors. Preston Henry Tolth, 26, could be sentenced to a maximum of five years in federal prison, with credit for three years already served, under the conditions of the proposed agreement. U.S. District Judge Douglas Rayes asked Tolth during a hearing in Phoenix if