Seth Fontenot’s attorneys Friday took aim at prosecutors’ version of how their client shot at three young men in 2013, challenging Lafayette investigators’ methods and conclusions about whether Fontenot was a proficient enough marksman to deliberately kill Austin Rivault and wound two others.

But in a daylong session heavy on technical reports and esoteric expert witnesses, it was Dr. Christopher Tate’s testimony and his photos of Rivault’s autopsy that bought the courtroom to an emotional low.

Tate, a forensic pathologist, described how the 9 mm bullet Fontenot has admitted firing struck Rivault below the hairline at the back of his head, and exited near his right upper lip, blowing out some teeth as it tore through.

The jury of 10 women and two men, along with two alternates, viewed the photos on a screen that also was visible to Rivault’s family and family friends, who wiped their eyes and cried silently. Rivault’s dad, Kevin Rivault, stared at the big screen and shook his head.

Rivault had a slight build — 5 feet, 5 inches and 138 pounds — and didn’t yet have facial hair, Tate said.

“The cause of death was a gunshot wound to the neck in the manner of homicide,” Tate testified.

Fontenot faces life in prison if he’s convicted of first-degree murder. He is also charged with two counts of attempted first-degree murder. A grand jury handed up the charges weeks after he shot at a truck carrying the three teenagers about 1:45 a.m. Feb. 10, 2013. Fontenot told police he believed the teens had tried to break into his truck.

Besides killing Rivault, Fontenot shot two other 15-year-olds, Cole Kelley and William Bellamy. Two years later, they still carry the bullets in their bodies, as doctors have elected to leave them for now.

Prosecutors rested their case against Fontenot on Friday, and defense attorneys called their first witness.

Thomas Guilbeau and Katherine Guillot, Fontenot’s attorneys, have contested police investigators’ methods, along with the medical and logistical conclusions of what happened that early morning.

Guilbeau questioned Tate calling the killing of Rivault a homicide, asking how Tate can know what Fontenot intended when he shot.

Tate said homicide is one person intentionally killing another and that Fontenot knew there were human lives in that truck.

“We don’t have vehicles driven by robots,” Tate said.

Kelley and Bellamy are now 17 and the star quarterbacks on their Lafayette Catholic high school football teams. They testified this week they were taking Rivault home from a get-together when they drove past Fontenot, who, wearing only sneakers and boxer shorts, lay in wait for the boys he believed were thieves. Kelley and Bellamy testified they never stopped or left the truck from the time they left the friend’s home to when they arrived at Our Lady of Lourdes Medical Center seeking help for gunshot wounds.

Fontenot later told detectives he fired at the truck’s tailgate — only to scare them — when the truck was 6 feet to 8 feet away on Green Meadow Road.

Assistant District Attorney J.N. Prather and Guilbeau repeatedly clashed about how far away Fontenot was from the truck when he pulled the trigger. Prather has concentrated his questioning on the distance Fontenot told detectives he was from the truck when he started firing.

But Guilbeau has tried to cast doubt on that scenario. The defense attorney introduced a distance he calculated by using the 35 mph speed Kelley told police he was driving when the bullets started ripping through the truck. Guilbeau said that would have put the truck over 100 feet away by the time the third shot was fired.

Ballistics expert Richard Ernest, a defense witness, said Lafayette police did not opt to use a technique sometimes used by other crime scene investigators — re-enacting the event. He said Lafayette investigators could have brought the truck that carried the boys back to the shooting location for an investigation with more accurate conclusions.

The trial resumes Monday at 10:45 a.m.