In 1967, Diamond won tribal status for the Tiguas, and they were placed under a state trusteeship. Twenty years later, he pushed through the congressional Ysleta Del Sur Pueblo (Tigua) Restoration Act to put them under federal control. In 1993, Diamond tried two cases before the Indians’ Claim Commission for the Tiguas and the Alabama Couchatta tribes. He again represented the Tiguas in 1999 when the State of Texas sought to have the tribal casino closed.