The man police say carried out a deadly shooting spree at the Fort Hood military base last week was charged with 13 counts of premeditated murder on Thursday.
Chris Grey, a spokesperson for the Army's criminal investigation agency, told reporters that more charges may be filed against Maj. Nidal Malik Hasan as the criminal investigation proceeds.
Hasan, a 39-year-old U.S. Army psychiatrist, is suspected of killing 12 soldiers and one civilian following a string of shootings in Fort Hood, Texas, on Nov. 5. Twenty-nine others were injured in the rampage.
Witnesses said two civilian police officers at the base eventually shot and wounded Hasan, bringing the violence to an end. He is now recovering in a San Antonio hospital, where his lawyer said he was read the charges.
None of the charges against him have been proven in court.
Earlier this week, U.S. President Barack Obama and his wife Michelle delayed an official trip to Asia to attend a memorial for those who were killed in the shootings. Obama told the victims' families that their loved ones "will endure through the life of our nation."
Thousands of civilians, soldiers and politicians were present at the memorial, which took place at Fort Hood on Tuesday.
Hasan was shot three times, reportedly by a female police officer. He has been taken off a respirator in hospital and is believed to be awake and talking.
As they build their case against Hasan, investigators are trying to determine what motivated him to allegedly shoot so many people on the military base where he worked.
Links are emerging between Hasan and a radical Islamic cleric in Yemen, who had previously preached at a mosque in Virginia.
Hasan came to the attention of the FBI in December when the agency learned he had exchanged between 10 and 20 emails with the cleric Anwar al-Awlaki, and attended services at his mosque before he left the U.S. for Yemen in 2002.
Alvear said the FBI determined their communications to be benign, and consistent with research Hasan would do as part of his work as a military psychiatrist who counselled troops returning from war.
Still, Obama has ordered a full review of Hasan's intelligence file to ensure that information was properly shared between agencies. The probe's findings are due on Nov. 30.
Some of Hasan's colleagues at the base have said they were concerned that he did not belong in the military.
While he was a student in a military medical program, classmates complained to their instructors after he expressed anti-American views. But they stopped short of filing a formal complaint in order to avoid the appearance that they were discriminating against a Muslim colleague.
But Hasan's family has defended his character.
"I've known my brother Nidal to be a peaceful, loving and compassionate person who has shown great interest in the medical field and in helping others," his brother, Eyad Hasan, wrote in a statement released on Saturday. "He has never committed an act of violence and was always known to be a good, law-abiding citizen."
CTV's Joy Malbon said that Nidal is still in hospital and is reportedly partially paralyzed. She added that the case will be tried in the military justice system.
"This whole process could take a very long time," Malbon said from Washington, adding that the charges were met with a sense of relief among many military personnel in the U.S.
Still, Malbon noted that Hasan's military lawyer could stall proceedings by asking that the judge transfer the case to another jurisdiction. The lawyer may also seek psychological evaluations before the trial begins, Malbon said.
With files from The Associated Press
