TACOMA, Wash. - A US soldier who killed five fellow servicemen in a shooting spree at a combat stress center in Iraq acted with the tactical precision of a trained soldier as he moved through the clinic, an Army crime scene expert testified on Thursday.

US Army Sergeant John Russell pleaded guilty last month to killing two medical staff officers and three soldiers at Camp Liberty in Baghdad in a 2009 shooting the military has said could have been triggered by combat stress.

Russell faces an abbreviated court-martial at Joint Base Lewis-McChord in Washington state, where a military judge will determine the level of his guilt. Russell's sentence will hinge on whether he acted with premeditation, as prosecutors say, or on impulse, as the defense argues.

An Army forensic science officer on scene after the attack testified on Thursday in the fourth day of court-martial proceedings that Russell had acted with tactical precision.

In one instance, the expert said, Russell avoided a splotch of blood next to a victim that his boots would have tracked about the room. In another, after taking two wayward head shots at a fleeing clinic worker, Russell dropped to his knee, bringing his "sight picture down to center mass like a good soldier" and fired again upon the worker, who survived.

"(This was) a deliberate, methodical, complex hunt throughout the building, sir," said Phillip Curran, an Operations Officer in the 11th Military Police Battalion, also known as the Criminal Investigation Command.

"There was nothing disorganized about it," Curran said.

Army prosecutors said Russell tried to gain a quick exit from the Army and had sought revenge on a mental health worker who would not help him achieve that goal.

STATE OF MIND

Prosecutors have called witnesses who described the more than 40 minutes Russell had to consider his actions as he drove to the clinic in a stolen Ford SUV and M16-A2 rifle, how he removed identification tags and the gun's optic, and have described him as having a stone-faced demeanor.

Russell's state of mind during the attack, one of the worst episodes of soldier-on-soldier violence in the Iraq war, has been central to legal proceedings over the past year at the Pacific Northwest military base, one of the nation's largest.

In a roughly 15-minute opening statement, a defense attorney said Russell's mental health, weakened by several combat tours, deteriorated further as those around him sought to "impose order on a chaotic situation."

"Russell acted on that one, single, solitary wish of a suicidal mind: the wish to kill," said Captain Benjamin Hillner, the defense attorney. "This inherent wish to kill ... that's not a wish to premeditate."

"No one is going to be able to say why Sergeant Russell went back to the combat stress clinic," Hillner said. "Everybody thought he was going to kill himself."

Hillner said a forensic psychiatrist, Dr. Robert Sadoff of the University of Pennsylvania, who previously concluded that Russell suffered from post-traumatic stress disorder and psychosis at the time of the shootings, would testify that the soldier had death wishes related to his illnesses.

Sadoff has suggested Russell was provoked to violence by maltreatment at the hands of mental health personnel he sought for treatment at Camp Liberty.

Russell, who agreed to plead guilty in a deal that will spare him the death penalty, faces up to life in confinement without the possibility of parole, forfeiture of pay and a dishonorable discharge. The judge will likely issue the sentencing next week.