U.S. Army officials say the alleged gunman in last week's shooting rampage at Fort Hood - Major Nidal Malik Hasan - has been charged with 13 counts of premeditated murder.
Chris Grey, a spokesman for the Army's criminal investigation division, announced the charges Thursday at Fort Hood.
Grey said it is possible that additional charges could be added as the investigation continues.
Hasan allegedly opened fire on unarmed soldiers at the Fort Hood military base as the troops were preparing for deployments to Iraq and Afghanistan.
Authorities are investigating motives for the attack amid concerns that U.S. authorities missed warning signs that could have prevented the rampage that left 13 dead and 30 wounded.
A group of U.S. military doctors overseeing Hasan's training as an army psychiatrist expressed concerns a year ago about his bizarre behavior.
Hasan, who was shot multiple times by civilian police during the attack, is recovering at an Army hospital near San Antonio, Texas.
Earlier this week, doctors said Hasan is in serious condition but is awake and talking.
U.S. media reports Wednesday, citing unnamed military officials, said the doctors that reviewed Hasan a year ago held a series of meetings where they discussed problems with his performance and mental state.
Colleagues described Hasan as aloof, belligerent and frequently argumentative when discussing his Muslim faith.
The officials decided against seeking his removal because they did not believe him to be violent and they thought his transfer to Fort Hood in July would help lessen his workload.