A US soldier accused of killing five fellow servicemen in Baghdad in 2009 was psychotic and suffered from post-traumatic stress disorder during the shooting frenzy, a top US forensic psychiatrist says.
Russell, of the 54th Engineer Battalion based in Bamberg, Germany, faces five charges of premeditated murder, one charge of aggravated assault and one charge of attempted murder in connection with the May 2009 shootings.
Six months ago, he was ordered to stand trial in a military court that has the power to sentence him to death, if he is convicted.
Russell's civilian attorney, James Culp, entered no plea at an arraignment on Monday at a military base in Washington state. Russell's court martial is tentatively set for mid-March and could last four to five weeks.
In a second day of hearings to discuss Russell's state of mind at the time of the shooting and establish what evidence or testimony to admit at the court martial, Robert Sadoff, a University of Pennsylvania forensic psychiatry expert, gave the opinion that Russell was suffering from post-traumatic stress disorder.
Russell has "dissociative disorder", or a lack of memory about the shootings, said Sadoff, who examined Russell for a total of 20 hours after the shootings. "He cannot remember. It's a legitimate disorder. He also has post-traumatic stress disorder."
Sadoff, a veteran of 10,000 criminal cases added: "It's a matter of what's going on in this man's mind. He was psychotic. He was not dealing with reality. That's what psychosis is."
If the defence can persuade a jury that Russell was not in control of his actions, it may be able to argue that he is not legally responsible and could spare him from the death penalty, if convicted.
During the hearing, Culp sought authority from Judge Colonel David Conn to hire a forensic hypnotist to unlock Russell's buried memories and conduct a specialised magnetic resonance imaging (MRI) test to measure Russell's "mild diffused brain atrophy", which Culp argues played a part in his behaviour.
This would help diagnose "the extent of brain damage as it relates to criminal responsibility," Culp said.
Army prosecutors urged the judge to decline. Major Dan Mazzone, one of four Army attorneys prosecuting the case, told the judge that an Army medical review already indicated that Russell's brain atrophy was typical of a man his age and further testing is an unnecessary expense to the Army.
"The bottom line, this is just not necessary. It's something the government should not be entitled to fund," Mazzone said.
The judge is set to rule on the matter over the next few days.
The proceedings, held at Joint Base Lewis-McChord near Tacoma, Washington, come at a sensitive time for the Army, which is in the process of deciding how to prosecute Staff Sergeant Robert Bales, a soldier accused of killing Afghan villagers in cold blood earlier this year.
A two-week hearing at Lewis-McChord to establish if there is sufficient evidence to send Bales to a court martial wrapped up last week after harrowing testimony from Afghan adults and children wounded in the attack.
Bales' civilian defence lawyers have also suggested he was suffering from post-traumatic stress disorder.
On Monday, Russell's attorney outlined a defence based on his declining mental state.
Russell suffered from depression, thoughts of suicide, anxiety and stress from multiple deployments, and suffered "at least one traumatic experience involving civilian casualties" and "mass grave sites" while serving in Bosnia and Kosovo during 1998 and 1999, Culp said in presenting arguments to the judge after the arraignment.