McKINNEY – For the first time, Jackie Mull eyed her sister's killer. It was only a second. But her hazel eyes met Kosoul Chanthakoummane's brown ones as she told him that the bad choices he had made would lead to his own death. Mrs. Mull took the witness stand Wednesday after a Collin County jury sentenced Mr. Chanthakoummane, 27, to die for the 2006 robbery and slaying of McKinney real estate professional Sarah Walker. Mrs. Mull did not cry or get emotional, a stark contrast to the previous day when she testified during Mr. Chanthakoummane's capital murder trial.Story....