A soldier accused of murdering his roommate - a fellow Ranger who served with him in Afghanistan - went to trial Tuesday in a case that will touch on how combat affected both men psychologically. Spc. Michael A. McQueen II died of a single gunshot to the right temple in September 2006, in the apartment he began sharing with Sgt. Gary Smith just 20 days earlier. Smith threw the weapon, a .38-caliber revolver, into a nearby lake before calling 911. He was covered in McQueen's blood and had gunshot residue on his hands when he was arrested, and prosecutor John Maloney said he repeatedly changed his story to investigators.

"This is a homicide. Gary Smith is the person that did it," Maloney told jurors in his opening statement. "The most important thing you'll bring to your deliberations is your common sense."

Smith's attorney, Andrew Jezic, said McQueen, 22, committed suicide and Smith, despondent over the loss of his buddy, tried to cover up the circumstances of the death by removing evidence from the scene.

"There is no motive in this case. Zero," Jezic said.

Both sides concede there is no direct evidence McQueen was suicidal and no concrete motive for Smith to kill him. Although they dispute the closeness of the young men's friendship, the two had served together in Afghanistan and had partied together frequently in the brief time they lived in the apartment in Gaithersburg, about 20 miles outside of Washington.

Smith could get life without parole if convicted of first-degree murder. He and McQueen had been in a U.S. Army Ranger intelligence unit and met at Fort Benning in Georgia.

Jezic claims his 25-year-old client, who served in Iraq (web|news) and Afghanistan, suffers from post-traumatic stress disorder and slept with a gun underneath his pillow. According to court records, Smith claimed he saw a friend die in Iraq and was hit by a bullet himself, saved only by his protective body armor.

Jezic also plans to present evidence that McQueen was under psychological strain. McQueen, who was raised in Miami, returned from his third tour in Afghanistan about two months before his death.

"He wasn't enrolled in school, he wasn't employed and he was drinking heavily," Jezic said. He cited evidence that McQueen's blood-alcohol concentration was between 0.13 percent and 0.20 percent at the time of his death, well above the 0.08 legal limit for driving.

"He was dealing with some tremendously difficult issues," Jezic said.

Prosecutors and McQueen's family dispute that claim, characterizing him as a fun-loving man with a bright future who was preparing to enroll at the University of the District of Columbia.

Prosecutors said McQueen was not particularly close with Smith, a native of nearby Derwood, and agreed to share an apartment with him only after Smith's plans to live with another friend fell through.

In afternoon testimony, Mike McQueen, father of Michael McQueen, said his son never told him he was living with Smith. McQueen also said he had never heard Smith's name until after his son died.

Mike McQueen is the New Orleans bureau chief for The Associated Press.

Maloney told the jury that during a lengthy interview with homicide detectives, the video of which will be played during the trial, Smith gave different accounts of his roommate's death.

Smith initially said he had not been in the apartment when McQueen was shot, but changed his story after detectives suggested that perhaps McQueen killed himself, Maloney said.

"He tells the story over and over again," Maloney said. "Each telling, he cannot keep the facts straight."

Maloney said a blood-spatter expert will testify that blood found on the carpet next to where McQueen died and on Smith's shoe indicates that Smith was right next to McQueen when McQueen was shot.

Jezic plans to call his own experts to dispute those claims, saying the blood spatter and gunshot residue are consistent with suicide and indicate that Smith could not have been close enough to McQueen to have shot him. He also told jurors that McQueen's arm was raised when he was shot.

Maloney showed graphic crime-scene photos to the jury. When McQueen was shot, he was sitting in a folding chair, wearing a white T-shirt and shorts. A beer bottle, marijuana and drug paraphernalia and a video game controller sat on the floor. Some of McQueen's relatives averted their eyes when the pictures were shown, while his father stared straight ahead.