Staff Sgt. Robert Bales, 38, was brought to the military prison at Fort Leavenworth, Kan., late Friday. Military officials said formal charges could come later this week, the report said.
The Seattle attorney retained to defend him traveled to Kansas Sunday and planned to meet Monday with Bales, the Journal said.
Bales's lawyers haven't denied the charges, but said they wanted to look at his military service to determine what factors might have influenced him.
Bales served three tours in Iraq and a tour in Afghanistan. He suffered traumatic brain injury as well as a severe foot injury.
"It is too early to determine what factors may have played into this incident and the defense team looks forward to reviewing the evidence, examining all of Sergeant Bales's medical and personnel records, and interviewing witnesses," lawyers, led by Seattle attorney John Henry Browne, said in a statement.