Staff Sergeant Robert Bales has been charged with 17 counts of premeditated murder over the March 11 slaughter in Kandahar Province.
He is currently being held in a military prison in the U.S. state of Kansas.
In his new comments, his lawyer, John Henry Browne, gave no details about the traumatic incident experienced by Bales in Iraq.
He also downplayed reports Bales had confessed to the Afghan killings and said there was no solid evidence in the case.
The lawyer has previously said Bales has only a sketchy memory of the night of the massacre.