A US soldier accused of killing 16 Afghan civilians after slipping away from his base will undergo a court-ordered review of his sanity this weekend.
Robert Bales' mental health has been expected to be a key part of his defence.
The military judge overseeing the case agreed that the results would not automatically be shared with prosecutors, lawyers for Bales said.
The review of Bales by US Army doctors will start on Sunday and could last three to seven days, lawyer John Browne said. Such reviews are aimed at determining a defendant's mental state at the time of the crime and competency to stand trial.
The staff sergeant is accused of murdering Afghan villagers, mostly women and children, during a pair of pre-dawn raids on March 11 2011. Bales, on his fourth combat deployment, slipped away from his base in southern Afghanistan to attack two nearby villages and returned soaked in blood, prosecutors say. He has not entered a plea. The army is seeking the death penalty.
Bales' lawyers previously objected to the sanity review because the army would not allow the proceedings to be recorded, let Bales have a lawyer present or agree to appoint a neuropsychologist expert in traumatic brain injuries to be involved.
They also objected because the "short-form" results of such exams are often provided automatically to military prosecutors, with the rest being turned over only if the accused raises mental health as a defence.
At a hearing in January, the judge ordered the sanity review to go forward. His written order later made clear that the prosecutors would not receive the short-form results, said Emma Scanlan, another lawyer for Bales. "They're not going to get that information, which is why our client is agreeing to participate," she said.
Mr Browne has previously said the defence team has obtained medical records indicating Bales had suffered from a traumatic brain injury and post-traumatic stress disorder, but he described those records as incomplete.
Last week, six Afghan civilians who are expected to give evidence at Bales' trial travelled to the military base in Washington state. Among the visitors was Haji Mohammad Naim, who was wounded during the massacre, said Lela Ahmadzai, an Afghan film maker who said she spoke with relatives of the victims recently.