Hasan has been identified as responsible for the killing of 13 people and wounding of 30 more in the mass shooting at the Fort Hood base.
Before the killings, the military psychiatrist was caught on camera shopping at a convenience store at the base, in CCTV footage unearthed by US broadcaster CNN.
After it was filmed, Hasan, armed with two handguns, walked into a training centre and opened fire on fellow soldiers who were having last-minute medical check-ups before being deployed to Afghanistan. Thirteen were killed and 30 injured.