Bales' civilian lawyer, John Henry Browne, has told The Associated Press that he met with Army officials last week to argue that his client shouldn't face the possibility of the death penalty, given that Bales was serving his fourth deployment in a war zone.
Browne didn't immediately return an email seeking comment Wednesday.
Bales' wife, Kari Bales, said in a statement released Wednesday that she hopes her husband receives an impartial trial.
"I no longer know if a fair trial for Bob is possible, but it very much is my hope, and I will have faith," she said.
Bales' defence team has said the government's case is incomplete.
Outside experts have said a key issue will be to determine if Bales suffered from post-traumatic stress disorder. Bales served tours of duty in Iraq and Afghanistan.
During last month's preliminary hearing, prosecutors built a strong eyewitness case against the veteran soldier, with troops recounting how they saw Bales return to the base alone, covered in blood.
Afghan witnesses questioned via a video link described the horror of that night. A teenage boy recalled how the gunman kept firing as youth scrambled, yelling: "We are children! We are children!" A girl recalled hiding behind her father as he was shot to death.
An Army criminal investigations command special agent testified that Bales tested positive for steroids three days after the killings, and other soldiers testified that Bales had been drinking the evening of the massacre.
Several soldiers testified that Bales returned to the base alone just before dawn, covered in blood, and that he made incriminating statements such as, "I thought I was doing the right thing."
Prosecutors, in asking for a court-martial trial, have said his comments demonstrated a "clear memory of what he had done, and consciousness of wrongdoing."
The US military has not executed anyone since 1961. Five other people in the US currently face military death sentences, all for murders committed stateside.
For Bales to face execution, the court martial jury must unanimously find him guilty of premeditated murder; that at least one aggravating factor applies, such as multiple or child victims; and that the aggravating factor substantially outweighs any extenuating or mitigating circumstances.
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Johnson can be reached at https://twitter.com/GeneAPseattle
-AP