Specialist Braden Purrentine of the first Cavalry trains a horse in front of flags flying at half mast at the Fort Hood Army Post in Fort Hood

Specialist Braden Purrentine of the first Cavalry trains a horse in front of flags flying at half mast at the Fort Hood Army Post in Fort Hood, Texas November 7, 2009. Investigators searched on Friday for the motive behind a mass shooting at a sprawling U.S. Army base in Texas, in which an Army psychiatrist trained to treat war wounded is suspected of killing 13 people. The suspected gunman, Major Nidal Malik Hasan, a Muslim born in the United States of immigrant parents, was shot four times by police, a base spokesman said. REUTERS/Jessica Rinaldi (UNITED STATES MILITARY CRIME LAW HEALTH POLITICS SOCIETY)