Bales, 38, allegedly gunned down nine Afghan children, four men and four women as they slept. The majority were shot in the head, chest and groin.
The 10-year Army veteran remains in custody in a military prison at Fort Leavenworth, Kansas.
Bales was also charged with the attempted murder of six other civilians - four children, an man and a woman. The wounded were treated by U.S. medical teams in Afghanistan. Two have been released, but four remain in medical care.
Bales' attorney says the soldier doesn't remember anything between the time he left the base and the time he returned.
"There is no crime scene, there's no CSI stuff, there's no fingerprints, there's no ballistics, they don't have the bodies," Brown said.
But there are images of investigators at the scene collecting evidence.
"There are investigators looking through the ground, presumably looking for shell casings, looking for other identifying information that would tie Sgt. Bales to the location," said former military lawyer Richard Meister.
The trial will be held in his home base of Fort Lewis, Washington. Afghan officials have asked for some role in the criminal proceedings, perhaps as observers, and to be kept up to date on the process of the case.
President Hamid Karzai has not demanded that Bales be turned over to the Afghan justice system, although some in the country's parliament did.
The shooting rampage was the worst allegation of civilian killings by an American and has severely strained U.S.-Afghan ties at a critical time in the decade-old war.
Bales, a father of two from Lake Tapps, Washington, was on his fourth tour of duty, having served three tours in Iraq, where he suffered head and foot injuries.
The Associated Press contributed to this report.
