DENVER — A Denver man who pleaded guilty to killing his wife while he was high on marijuana edibles was sentenced Friday to 30 years in prison.

Richard Kirk, now 50, pleaded guilty in February to second-degree murder, changing his not-guilty-by-reason-of-insanity plea in the April 14, 2014, homicide. He was set to go to trial on first-degree murder charges and was facing life in prison.

Kirk shot his 44-year-old wife, Kristine, in the head while she was on the phone with a 911 operator, telling that person she was scared because her husband seemed drunk and was going into their gun safe. The couple's three sons were in the home when it happened.

The youngest, age 7, saw his father shoot his mother. Richard Kirk, married to his wife for 15 years, walked into the child's room and tried to hand the gun to his son, asking the boy to kill him, police said.

As part of the plea agreement, Richard Kirk agreed to relinquish parental rights to his children. Kris Kirk’s parents have adopted them.

“Just recently he’s been able to go to bed alone a few times a week,” said Kris Kirk's mom, Marti Kohnke, said of the youngest child, now 10. “For a number of years, I would lay next to him. I would tell him stories.

"He would beg me to get the picture out of his head," Kohnke said. " ‘I can’t get the picture out of my head. Can you just help me get that picture out of my head?’ he’d ask."

Police found a receipt for marijuana-infused candy and a partially eaten Karma Kandy Orange Ginger chew in the family's home.

If Richard Kirk had gone to trial, his defense team was planning to claim that the marijuana caused delirium and psychotic symptoms. Though police also found an empty bottle of an opioid pain killer, hydrocodone, in the house, toxicology tests later found that Richard Kirk had only a small amount of THC, the psychoactive ingredient in pot, in his system.

One piece of Karma Kandy has more than 100 milligrams of THC; 10 milligrams is Colorado's definition of one edible dose of THC.The state's legal threshold to be considered driving impaired is 5 nanograms of THC per milliliter of blood; Richard Kirk's test results showed 2.3 nanograms.

The Kirks' sons have a wrongful-death lawsuit pending against the company that manufactured the edible and the store where Richard Kirk bought the candy.

The Kohnkes say that all was not well with the Kirks' marriage before Richard Kirk killed their daughter. They witnessed his emotional abuse toward her and never really got along with their son-in-law.

Three months before the shooting, Kris Kirk told her parents that she was going to leave her husband. But it was not clear whether she ever told Richard Kirk.

“Our lives changed 100%” after the shooting, said Kohnke, who's 70. “We now have the responsibility of putting three boys through college, raising three children. It’s a heavy responsibility and a very big worry."

They now are ages 16, 14 and 10.

Marti and Wayne Kohnke worry about their age — and living long enough to make sure that the boys grow to adulthood. If they die, Kris Kirk's sister, Tammy Heman, will be their new mom; she left her job right after the shooting to take care of the boys.

Now the Kohnkes' hope that Richard Kirk's 30-year sentence and five years of probation will be enough to keep the boys' father incarcerated until the children are well into adulthood. They agreed to the plea deal so the children would not have to testify against their father.

“People tell us we’re remarkable and all that. We’re not,” Marti Kohnke said. “We are just a normal family. Wayne and I. I don’t believe there’s any grandparent out there who wouldn’t do what we have done.”