Tyler Naughton, 19, was sentenced Friday to 25 to 30 years in prison by Third District Payette County Judge Susan Wiebe.
"I was pleased with her sentence. It was well thought out," Payette County Prosecuting Attorney Anne-Marie Kelso said.
Naughton pleaded guilty in July to voluntary manslaughter. In exchange, a felony grand theft charge was dismissed.
Sherryl M. Kenney, 60, Naughton's paternal grandmother, was found dead inside her home south of Fruitland on Sept. 2, 2012. She had been shot four times with a .22-caliber gun.
Hours later, Naughton was discovered in Adams County driving Kenney's pickup, which had been stolen.
Michael Kenney, Sherryl Kenney's husband, did not testify at trial and did not provide the court with a victim impact statement Friday.
Kelso told the judge that Michael Kenney is wanted on a warrant for lewd and lascivious conduct. He is accused of sexually abusing Naughton when he was a minor.
The defense told Wiebe that Naughton had also been physically abused by step-parents while he was growing up.
Naughton faced up to 30 years in prison on the manslaughter charge, plus up to an additional 15 years for an enhanced sentence because of the use of a firearm in the killing.
Kelso asked for Naughton to spend 30 years in prison.