Bales, 39, is accused of 16 counts of murder, six counts of attempted murder and seven counts of assault.
In a news release Wednesday, the Army said Bales could be sentenced to death but acknowledged it may be difficult for the prosecution to win such a sentence, ABC News reported.
"For capital punishment to be imposed, the court-martial members must unanimously find: the service member is guilty of the eligible crime; at least one aggravating factor exists; and that the aggravating factor must substantially outweigh any extenuating or mitigating circumstances found by the court-martial members," the release said.
The (Tacoma, Wash.) News Tribune reported in June recent history of military capital cases suggests juries are reluctant to impose capital punishment in crimes committed in a combat zone. In addition, the Army has not carried out an execution since 1961.
Army prosecutors allege Bales left Camp Belambay in Kandahar province twice the night of March 11 to kill residents of the villages of Alkozai and Najiban. They said the slayings were retaliation for an improvised explosive device attack several days earlier on a detachment of Army special forces troops.
Prosecutors said Bales was covered in blood and carrying a rifle, a 9-millimeter pistol and a grenade launcher when he was arrested returning to camp about 4:30 a.m.