As its last witness, Gary Smith’s defense team called Vincent Di Maio, a forensic pathologist, former military wound specialist, chief medical examiner in San Antonio for 25 years, editor of the American Journal of Forensic Medicine and author of a book called “Gunshot Wounds.”

His conclusion in the shooting death of Michael McQueen?

“This was a self-inflicted wound,” Di Maio said.

To a rapt jury in Rockville, he testified that he had considered three aspects of the case of the two former Army Rangers who served together in Afghanistan and shared an apartment in Gaithersburg, where the shooting took place in September 2006.

Smith is charged with “depraved-heart” second-degree murder, for which prosecutors must show that he shot McQueen and acted with “extreme disregard” for human life. But on the witness stand in Montgomery County Circuit Court was the defense’s star witness, contesting that contention without reservation.

First, he said, he had examined the circumstances surrounding the death and found no history of “arguments or fights” between the former soldiers and nothing conclusive to suggest that McQueen was depressed and possibly suicidal.

Next, he reviewed Smith’s “bizarre” behavior after the shooting, in which he first denied being at the scene when it happened, then admitted that he was there and ultimately confessed to throwing the gun that caused McQueen’s death in a lake.

Smith was either acting to “conceal a crime,” Di Maio said, or he was “a drunk young guy who panicked.”

But in the third area of examination — the physical evidence and autopsy — Di Maio expressed no such ambivalence: “This is a single gunshot wound to the right temple.”

He said the “trajectory is the normal trajectory you see in a self-inflicted wound. . . . You point backwards and upwards. This you see in virtually all self-inflicted wounds.”

Di Maio said he and his colleagues had collected information on 1,704 suicides by gunshot from 1984 to 1998, including materials on the wounds, toxicology reports, and whether there were suicide notes, among other things. He said 97.9 percent of the wounds were contact wounds; 83.7 percent were head wounds; 50 percent of the wounds were in the right temple; and 31.9 percent of the suicides involved alcohol. “In this case, we had contact, right temple” and a blood-alcohol reading of 0.13 percent at the time of autopsy.

On cross-examination, Deputy State’s Attorney John Maloney pressed Di Maio on how much he had been paid as a defense witness and sparred with him aggressively on what he said were inconsistent and faulty conclusions.

Maloney also asked Di Maio how he could conclude from Smith’s disposing of the gun that McQueen had committed suicide.

Smith, Di Maio replied, had not otherwise altered the crime scene. He could have removed the body or tried to conceal it. But he didn’t do either of those things.

The defense rested after his testimony.

The prosecution will call rebuttal witnesses Friday, defense attorneys will cross-examine them, and closing arguments will follow. Judge Eric M. Johnson told jurors that they should expect to get the case by day’s end.

For comprehensive coverage of the trial, go to crime.