Maj. Nidal Malik Hasan, the alleged Fort Hood gunman and a psychiatrist who worked in a hospital at the base, is blamed for the deaths of 12 soldiers and one Army civilian employee, and for wounding at least 38 others.
If convicted, Hasan will join an infamous list of Americans who have committed acts of mass murder.
Since 2005, there have been at least 11 other incidents where gunmen have opened fire on groups of victims.
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