By Anita Snow THE ASSOCIATED PRESS PHOENIX (AP) _ U.S. Border Patrol agents answering reports of gunfire fatally shot a man on a tribal reservation in southern Arizona last week after he abruptly threw something and raised his arm, the agency said. This is CPB’s first detailed accounting of the shooting near the U.S.-Mexico boundary. The FBI and Tohono O’odham Nation are also investigating the fatal shooting of Raymond Mattia on Thursday. Neither agency had released details about the shooting by Tuesday. The statement released Monday night by U.S. Customs and Border Protection said tribal police had asked Border Patrol agents for help in responding to a report of shots fired west of the Menagers Dam community on tribal land near the U.S. southern border. The village is on the…