MEXIA, Texas (AP) — Officials say a Texas state trooper who was shot during a traffic stop last week is not expected to survive. Trooper Chad Walker is being kept on life support to be an organ donor, according to the Texas Department of Public Safety. The agency says on Twitter that Walker no longer shows signs of “viable brain activity.” DPS regional director Todd Snyder says Walker was shot Friday while stopping to help a driver in an apparently disabled vehicle west of the city of Mexia. Snyder says Walker had not yet stopped behind the vehicle when 37-year-old DeArthur Pinson got out and opened fire. Authorities say Pinson later killed himself.