US First Lady Michelle Obama and President Obama walk past the Fallen Hero Memorial at Fort Hood on November 10, 2009 during a service honoring the soldiers and civilians killed in a shooting rampage on November 5. US Army Major Nidal Malik Hasan, 39, a psychiatrist and specialist in combat stress, who allegedly killed 13 people and wounded 42 in a shooting rampage at Fort Hood, is believed to have acted alone by investigators and no motive has been established.