Prosecutors in Gary Smith's retrial said in opening statements Thursday that evidence will show that Smith killed his roommate, a fellow Army Ranger with whom he served in Afghanistan, in their Gaithersburg apartment.

But a defense lawyer said in Montgomery County Circuit Court in Rockville that he believes the second murder trial will show that the victim, Michael McQueen, killed himself -- either accidentally or in a suicide.

In September 2006, McQueen died of a gunshot wound to the head in apartment that he and Smith shared.

Smith, now 29, is charged with depraved-heart second-degree murder -- a killing committed while acting in "extreme disregard" for human life -- as well as with use of a handgun in the commission of a crime. The murder charge also has a lesser-included charge of involuntary manslaughter.

In 2008, Smith was convicted of depraved-heart murder and the handgun charge but was acquitted of first-degree murder and intentional second-degree murder. He was sentenced to 35 years in prison.

But the Maryland Court of Appeals overturned Smith's conviction in 2011, ruling that jurors should have been able to hear testimony from the police officer who arrested McQueen for drunk driving the month before his death because it showed evidence of a depressed state of mind.

McQueen allegedly told the arresting officer that he didn't need the arrest with everything else going on in his life. Defense Attorney Barry Helfand mentioned this remark during his opening statement Thursday. The victim's mother, Glenda McQueen, testified that her son was optimistic and refuted the notion that he would take his own life.

"I don't believe he would commit suicide," she said, though she said did not know about the drunk driving charge until after her son's death.

Deputy State's Attorney John Maloney described McQueen as an outgoing young man. Toward the end of his opening statements, Maloney showed jurors a photo of McQueen smiling.

The prosecution played video clips of Smith talking to detectives, with Smith changing his story about what happened on the night of his roommate's death. He first tried to paint the incident as a murder by a stranger, then said McQueen shot himself while Smith went out to pick up laundry at his mother's home. He then said that McQueen shot himself after Smith had returned from picking up the laundry.

Helfand said that forensic evidence would support that Smith's last version of the story was the truth.

"It was not a lie," he said.

If convicted, Smith could face up to 30 years for the murder charge and up to 20 years for the handgun charge, a State's Attorney's office spokesman said.