We are learning quite a bit about the Ft. Hood shooter . He was a psychiatrist from Maryland, a Muslim (maybe Syrian or Jordanian) and upset that he was being deployed to the Middle East:

Jeff Sadosky, a spokesman for U.S. Sen. Kay Bailey Hutchison, said the senator had been told that Malik Nadal Hasan, who has been identified as a the shooting suspect at Fort Hood, was upset about his upcoming deployment to Iraq or Afghanistan.
[…]
A defense official speaking on condition of anonymity says Hasan was a mental health professional — an Army psychologist or psychiatrist.

ABC News is saying that he was the only shooter and maybe a Syrian or Jordanian. The other two who were detained have been released. It’s looking more like a lone gunman scenario and less like a terrorist attack.
You can get updates on Twitter @FtHoodShootings.