This is WEEKEND EDITION from NPR News. I'm Rachel Martin. U.S. Army officials are saying that an argument may have set off Specialist Ivan Lopez, who went on a shooting rampage at Fort Hood this past week. He killed four people, including himself, and injured 16 others. Those who survived were taken to Baylor Scott and White Hospital nearby in Temple, Texas. Dr. Matthew Davis is the head of the trauma program there. He and his staff also treated the injured after the 2009 mass shooting at Fort Hood.