PHOENIX — A Phoenix woman who says her 2-year-old son fatally shot her 9-year-old son with a handgun that she left on a bed faces sentencing Thursday for her role in the killing that still puzzles investigators 2½ years later.

The plea deal for Wendy Lavarnia calls for a prison sentence of 10 to 16 years for manslaughter in the shooting death of her son, Landen. She acknowledged at a plea hearing a month ago that she caused his death by recklessly leaving the gun out where the toddler could grab it while the children played a video game.

In the months after the March 2017 killing, Phoenix police expressed skepticism about Lavarnia’s account and said they were having a tough time determining who shot the child. Lavarnia and her husband also were accused of delaying medical care for Landen, though that charge was later dismissed.

Prosecutors still can’t determine who fired the gun, said Amanda Steele, a spokeswoman for the Maricopa County attorney’s office.

Wendy Lavarnia. Maricopa County Sheriff's Office

Wendy Lavarnia had told police that she put her loaded gun on a bed at her house within reach of her children and then turned away to get something. She denied firing the gun.

“I got my gun down and left it on the bed like an idiot,” she told an operator during a 911 call. “And my son _ I didn’t think he could fire it, and he shot it.”

Police say Lavarnia’s husband, Kansas Lavarnia, showed up at the house after the shooting with a crudely bandaged gunshot wound on his upper arm, which looked to have been punctured multiple times — possibly with a screwdriver — to camouflage the injury.

He claimed to be out shopping when the shooting happened and returned home after police arrived.

Police accused the couple of delaying medical care for their son to clean up evidence in the house, noting that a lack of visible blood implied a long time had passed before they called authorities.

Fourteen months after his son’s death, Kansas Lavarnia killed himself, on Father’s Day 2018.

Shortly before his suicide, Lavarnia told The Arizona Republic that he was at home during the shooting and had fled because he had prior criminal convictions that barred him from possessing guns.

Lavarnia told the newspaper that the shot fired by his 2-year-old son struck him in the upper part of his left arm, causing the bullet to fragment and leading police to believe the wound was made by a screwdriver. He said one of the fragments then exited his arm and struck Landen in the head.

Originally, the couple were each charged with murder, child abuse and hindering prosecution in their son’s death. Prosecutors later dropped the murder charge against Kansas Lavarnia.

Wendy Lavarnia’s plea deal reduced her murder charge to manslaughter and one of her child abuse charges to attempted child abuse. Her remaining counts will be dismissed at sentencing.

In a memo to the judge, her attorney, Clare Schum, said Lavarnia acted out of character and that the child’s death occurred during a momentary lapse of judgment.

A report attached to the memo said Lavarnia wants to re-establish a relationship with her children and their adoptive parents once she’s released from prison.