Authorities have not identified a motive in Thursday's attack that left 13 dead and 42 others wounded.
Hasan, a 39-year-old licensed Army psychiatrist who worked at a hospital on the post, has been identified as the suspected shooter. He was shot several times after the attack. On Sunday, he was listed in critical but stable condition and in intensive care at Brooke Army Medical Center in San Antonio, Texas.
Hasan's ventilator was removed over the weekend, and he began talking afterward, hospital spokesman Dewey Mitchell said. He is speaking with hospital staff, but Mitchell was unable to say whether Hasan has been speaking with Army investigators.
The development comes a day after Army investigators asked troops and civilians for help gathering clues about the shooting, saying some who fled the gunfire might have evidence.
"The Fort Hood office of the U.S. Army Criminal Investigation Command is seeking any military or civilian personnel who may have left the scene ... with gunshot damage such as damaged privately owned vehicles, personal clothing, etc.," investigators said in a written statement. "CID is also seeking any military or civilian personnel who may have inadvertently left the scene of this incident with material that could be used as firearms residue-related evidence such as shell casings inside the boot, etc."