FORT HOOD, Texas | An Army psychiatrist set to be shipped overseas opened fire at the Fort Hood Army post on Thursday, authorities said, a rampage that killed 12 people and left 31 wounded in the worst mass shooting ever at a military base in the United States.</p><p>The gunman, first said to have been killed, was wounded but alive in a hospital under military guard, said Lt. Gen. Bob Cone at Fort Hood. He was shot four times, and was on a ventilator and unconscious, according to military officials. &ldquo;I would say his death is not imminent,&rdquo; Cone said.</p><p>The man was identified as Maj. Nidal Malik Hasan, a 39-year-old, eight-year veteran from Virginia.</p><p>The shooter used two pistols, one of them semiautomatic. Neither were military-issued, Col. Ben Danner said.</p><p>President Barack Obama called the shooting at the Soldier Readiness Center, where soldiers who are about to be deployed or who are returning undergo medical screening, &ldquo;a horrific outburst of violence.&rdquo;</p><p> There was no official word on a motive in the rampage. Hasan had transferred to Fort Hood in July from Walter Reed Army Medical Center, where he received a poor performance evaluation, according to an official who spoke on the condition of anonymity because he was not authorized to discuss the case publicly.</p><p>Sen. Kay Bailey Hutchison, a Texas Republican, said generals at Fort Hood told her that Hasan was about to deploy overseas.</p><p>Terry Lee, a retired colonel who said he had worked with Hasan, told Fox News he was being sent to Afghanistan. Lee said Hasan had hoped Obama would pull troops out of Afghanistan and Iraq and frequently argued with others in the military who supported the wars.</p><p>Video from the scene showed police patrolling the area with handguns and rifles, ducking behind buildings for cover. Sirens could be heard wailing while a woman&rsquo;s voice on a public-address system urged people to take cover.</p><p>&ldquo;I was confused and just shocked,&rdquo; said Spc. Jerry Richard, 27, who works at the center, but was not on duty during the shooting. &ldquo;Overseas you are ready for it. But here you can&rsquo;t even defend yourself.&rdquo;</p><p>Families, so used to being separated during long deployments, were separated again in a situation that seemed surreal to many. </p><p>&ldquo;My friend&rsquo;s husband called her from Iraq and said, &lsquo;Isn&rsquo;t it sad that I am safer over here in Iraq than you are at home?&rsquo;&ensp;&rdquo; said Jessica Sullens, 28, who had spent hours in a nearby Wal-Mart parking lot, where she had dashed on an errand.</p><p>Her husband, Cpl. Thomas Sullens, and their 1- and 2-year-old daughters were in lockdown on the post. He was with his motor pool while the children were with a neighbor. &ldquo;This is unreal to me,&rdquo; Sullens said.</p><p> Soldiers at Fort Hood don&rsquo;t carry weapons unless they are doing training exercises.</p><p> The Rev. Greg Schannep was about to go into a graduation ceremony when a man in uniform approached him, warning him that someone had opened fire. Schannep heard three volleys of gunfire and saw people running.</p><p> &ldquo;There was a burst of shots and more bursts of shots and people running everywhere,&rdquo; said Schannep, who works for U.S. Rep. John Carter.</p><p> The uniformed man who had warned him ran to the theater. Schannep said he could see the man&rsquo;s back was bloodied from a wound. The man survived, Schannep said.</p><p> Cone said initially three people were held, and all have been interviewed. Authorities believe, however, that there was a single shooter.