Prosecutors in the homicide trial of Jeremey Sickenberger rested their case on Tuesday, after a morning of expert testimony focused on the .22-caliber rifle, a bullet from which shot and killed Thomas “T.J.” Stockman more than two years ago.

The commonwealth’s expert forensic firearm and tool mark examiner, state police Cpl. Robert Hagins, testified that the weapon — an older Rossi slide action .22 which lacks some safety features of more modern guns — was “forensically odd,” and had a strange, after-market alteration.

But, Hagins testified, he could only find one way to make it fire without pulling the trigger. That involved a specific setup in which the gun’s hammer — the mechanism which strikes the weapon’s firing pin and causes a bullet to fire — was left in a fully-forward position, the gun was loaded with a round in the chamber, and the hammer was struck sharply from behind.

Sickenberger, 25, is charged with criminal homicide in the shooting death of Stockman on April 17, 2014. His account of the events that evening has changed multiple times, but he has claimed the shooting was an accident, that he did not believe the gun was loaded, and that he does not remember if he pulled the trigger.

Hagins testified that the amount of force it takes to pull the weapon’s trigger — 3 pounds, 6 ounces — isn’t insignificant, but it’s lighter than the 4 pounds he recommends officers use on their duty weapons.

“It’s neither very light nor very heavy, Hagins testified regarding the weapon’s trigger pull.

But, he added: “I think you have to be really aware of what you’re doing. If you’re not aware of what you’re doing, that 3 pounds 6 ounces isn’t a lot of work.”

Many of Sickenberger’s friends and family were called to the stand by the defense. Two — Sickenberger’s father, Shawn Bennear and his friend, Michael Lively — were there the night Stockton was shot and testified to what they saw and heard. Neither saw the incident firsthand.

Bennear testified that he was in his room at the mobile trailer home on Robbie Way when Stockman was shot. Lively testified that he was in the home’s bathroom at the time, but heard both Sickenberger and Stockman talking about a BB gun before hearing the shot that killed Stockman.

Both testified that Stockman and Sickenberger were close friends — “like brothers,” said Bennear — and that they believed the shooting was unintentional.

Others, like Paul Pfaff, a U.S. Army veteran who owns the gun that killed Stockman, were called to the stand by prosecutors. Pfaff testified on Tuesday that he had left the .22 rifle and two other guns at Sickenberger’s home days before the shooting, and that he had told Sickenberger that the .22 rifle had ammunition in its magazine.

Defense attorney Joseph Smith pushed Pfaff to explain statements he made to state police during their investigation. According to a transcript of the interview, Pfaff told troopers he was “90 percent sure” the rifle wasn’t loaded, but also explained that he was referring to it not having a round in its chamber. He testified that he didn’t try to explain the distinction he was making to Sickenberger that night, but that Sickenberger knew the gun had ammunition in it.

Prosecutors rested their case after calling Dr. Leon Rozin, a forensic pathologist for Butler County, to the stand to review the results of an autopsy performed on Stockman the day after his shooting. Prosecutors, as part of the testimony, introduced four graphic photos showing Stockman’s body, the bullet wound to his chest, and his heart, which was pierced through-and-through by the .22 caliber bullet.

The display caused some members of Stockman’s family to leave the courtroom, and a member of Sickenberger’s family sobbed softly as Rozin’s testimony progressed. Sickenberger, who again appeared in court in a suit and tie, and was seated next to the television displaying the photographs, held his head in his hands and refused to look at some of the images.

Defense attorneys told Judge William Shaffer they expected to call at least two more witnesses to testify when the trial resumed this morning.