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Provo • When Joshua David Petersen shot and killed his infant son in April, his family members lost more than the 5-month-old child — they lost the 21-year-old man who pulled the trigger, who will now spend the rest of his life in prison.

"We lost two that day," Tammy Petersen, Joshua Petersen's mother, said during her son's sentencing Monday. "Our family will never be the same."

On Monday, Petersen was sentenced to life in prison without the possibility of parole for the April 5 slaying of Ryker Petersen. Though the sentence was already agreed upon as part of a plea deal, Joshua Petersen's family still had hope that 4th District Judge Darold McDade would allow the man an opportunity to be paroled in 25 years.

"We as a family feel this punishment is wrong," Tammy Petersen told the judge tearfully. "We are asking you to reconsider his sentence."

But McDade told Joshua Petersen that he worried if he had the chance to be paroled, he may harm someone again in the future, adding that coming to an appropriate sentence was difficult, given that Petersen's age and lack of criminal history would normally constitute a lesser sentence.

"It's just the circumstances and facts around this case that troubles me," McDade said. "… This has weighed on me as much as anybody else."

Joshua Petersen pleaded guilty in September to aggravated murder, a first-degree felony. Police say Petersen shot his son in the head with a .22-caliber rifle April 5, then tried to turn the gun on himself at his home near 500 East and 500 North in American Fork. A family member reportedly intervened before he was able to take his own life.

Tammy Peteresen told the judge that before the shooting, her son had never been in trouble, had never done drugs or drank alcohol and had never been in a fight.

But in the year before the shooting, her son spiraled into a deep depression.

"Josh was not himself [at the time of the shooting,]" the mother said, while her son sat nearby and sobbed. "How could he be? For whatever reason, Josh felt there was no help for his future, and he was terrified that he was going to lose his baby boy."

Tammy Petersen said her son had been on several antidepressants in the past year and was unstable on the medication he was taking on the day of the shooting.

Deputy Utah County Attorney Craig Johnson said Ryker Petersen's mother and her family — who did not address the judge during Monday's sentencing — were satisfied with the sentence.

"Certainly, the punishment fits the crime," Johnson said.

But for Joshua Petersen's family, watching the 21-year-old man receive the life sentence was difficult.

"This is a hard place for our family," Pam Thompson, Joshua Petersen's grandmother, said outside court. "I've lost my first grandson, and my first great-grandson."

Twitter: @jm_miller