Washington (CNN) -- A lawyer for Sgt. Robert Bales said Tuesday "there may be explanations" for the alleged shooting this month by his client of 16 Afghan civilians, but -- even if that is what happened -- the government will have a difficult time making its case.
"I don't know if the government is going to prove much," lead attorney John Henry Browne told CNN about the shootings of nine children, three women and four men in a village in southern Afghanistan. "There's no forensic evidence, there's no confessions."
He added, "Nothing really justifies killing women and children in a noncombat situation. But there may be explanations if that's true. And right now I want to say once again, I'm not sure that's true."
Bales, who had served three tours of duty in Iraq before being sent to Afghanistan, may have been suffering post-traumatic stress disorder, Brown said. Bales suffered a traumatic brain injury during a roadside bomb explosion and lost part of his foot in separate tours in Iraq, his attorney has said. "Anybody that has seen what he's seen and done what he's done at the request of the military -- and I'm not talking about these allegations -- I think would have PTSD ... Dragging parts of bodies around is not something you forget very often."
He said he expects his client to be charged on Thursday, probably with "homicide and a bunch of other charges," and predicted that the case would last two years.
But Browne denied that money woes could have led to Bales' alleged conduct.
"Sure, there's financial problems," Browne continued. "I have financial problems, 99% of America has financial problems. You don't go and kill women and children because you have financial problems."
Browne also denied that the soldier was drunk at the time of the shootings. "A couple of sips of somebody else's bottle," he said. "But that's not drinking."
He said he had met with Bales had met with three of his lawyers, including Browne, for 11 hours and that Bales was in shock and doesn't remember what happened. "That's common with concussive injuries," he said. 'You remember certain things; you don't remember other things."
The attorney said he will not pursue an insanity defense for his client, but one of diminished capacity, CBS reported.
The military will also conduct a separate investigation into the circumstances surrounding Bales' assignment to the combat outpost in southern Afghanistan, the top commander for U.S. and NATO troops in Afghanistan said Tuesday.
The administrative review, which will take place separately from the criminal investigation, will be conducted by U.S. Forces Afghanistan, Gen. John Allen told the House Armed Services Committee.
The investigation will consider how Bales was assigned and why he was assigned to the combat outpost, Allen said. "It will look at the command relationships associated with his involvement in that combat outpost," Allen said.
"He's a soldier's soldier," defense lawyer Browne said. "He didn't particularly want to go over there, and he could have used reasons not to, but he did as he was told."
A defense official told CNN Tuesday that the military had not started the probe. "It is in preparation to start soon," said the official, who was not authorized to speak on the record and asked not to be identified. "That is by design not to conflict with the criminal investigation."
The investigation will examine other administrative, training and command channels "to see if anything can be attributed to the incident," the official said.
The official said the investigation will go beyond Bales' time in Afghanistan and will look at deployment decisions and training he received prior to arriving in that country.
Bales, who is being held at the U.S. military prison at Fort Leavenworth, Kansas, stands accused in the killings in southern Afghanistan's Kandahar province, allegations that have strained already tense U.S.-Afghan relations and intensified a debate about whether to pull American troops ahead of their planned 2014 withdrawal.
After the shootings, which took place in two neighboring villages just outside a U.S. outpost in the Panjwai district, Afghan President Hamid Karzai demanded troops withdraw from villages and return to their bases. He said relations between the two countries were "at the end of their rope."
Afghans are insisting that the suspect be returned to Afghanistan to face trial, even as villagers and lawmakers question the U.S. military's account of what happened.
U.S. officials have alleged Bales left his outpost alone and carried out the killings in the villages alone.
U.S. Defense Secretary Leon Panetta has promised Karzai a full investigation and said the United States will bring the shooter to justice.
The trial will be held in the United States, though the location has not been decided, a U.S. Forces Afghanistan legal expert told reporters Sunday. "We will develop charges hopefully within the next week," said the expert, who would not speculate on what they might be.
Discussions are under way for the United States to compensate relatives of the victims, the expert added.
The government of Afghanistan will not be present in the court, the expert said in response to a question, but some Afghans may be taken to the United States for Bales' trial.
Accounts from the military, Bales' family, friends and neighbors paint a portrait of a man who bore scars from wounds he received during three previous combat tours to Iraq but remained committed to serving his country, and deployed to Afghanistan in January.
CNN's Michael Martinez in Los Angeles, Sara Sidner in Kabul, Afghanistan; Paul Vercammen in Auburn, Washington and Bill Kirkos contributed to this report.