(CNN) -- Special operations troops at a small military outpost in Afghanistan gave alcohol and steroid-like drugs to a U.S. Army sergeant accused of killing 16 Afghan civilians, the soldier's lawyer said Thursday.
Attorney John Henry Browne said the special operations troops "pumped" Staff Sgt. Robert Bales with the substances.
"He was provided all these things," Browne told CNN. "Special forces were in charge."
Bales is accused of murder in the death of the 16 civilians, including children, in March 2012. Prosecutors say Bales slipped off the base after dark and went from house to house, shooting villagers. In addition to the dead, six people were wounded.
Witnesses testified last year that Bales had consumed alcohol with other soldiers before the attack. He also was charged with illicit use of steroids and alcohol.
Browne said last year that "steroid use is going to be an issue in this case, especially where Sgt. Bales got steroids and how he got steroids."
Browne said Wednesday that Bales intends to plead guilty to the killings in exchange for elimination of the death penalty as a possible punishment.
If the deal is approved by the military judge and a commanding general, Browne will mount the argument about steroids and alcohol at a penalty phase hearing to determine whether parole will be a possibility as part the life sentence he could receive.
The Army would not comment on any potential deal Wednesday. A hearing in the case is scheduled for June 5.
Browne has previously said the Army erred in assigning Bales to another combat tour despite evidence of post-traumatic stress disorder and a traumatic brain injury suffered during a combat tour in Iraq.
Bales, he said Thursday, was a "broken man."
"We broke him. He never should have been there," he said.
Browne said he will bring experts in combat stress to the penalty phase hearing, despite the fact that the military has historically not accepted combat stress as the sole explanation for crimes committed by service members.
The strategy outlined by Browne is one he has pursued since taking on the case last year.
We think the Army is attempting to escape responsibility for the decision to send Sgt. Bales to Afghanistan for his fourth deployment, knowing that he had (post-traumatic stress disorder) and a concussive head injury," Browne said last year.
"I think that the person who made the decision to send Sgt. Bales to the most dangerous area in Afghanistan in a small outpost is responsible for Sgt. Bales being in Afghanistan, and he should have never been there."
The shooting spree strained already tense U.S.-Afghan relations and intensified a debate about whether to pull out American troops ahead of their planned 2014 withdrawal.
Afghan authorities have called for swift action.
"He committed a mass killing crime, and we would like the court in the United States to implement justice and punish him according to the crime," said Ahmad Zia Syamak, spokesman for Afghan President Hamid Karzai.