Dean Grenstiner Pleads Guilty to Killing Mother - KXNet - Bismarck/Minot/Williston/Dickinson

Dean Grenstiner pleads guilty to murder in the death of his mom, Ann Grenstiner.

The 83 year old woman was found dead in her Bismarck home in March.

Today during the change of plea hearing, details are revealed about the brutal beating that lead to Ann Grenstiner's death.

The last time anyone spoke to Ann Grenstiner, she was watching Dancing with the Stars on a Monday night.

A niece found Ann dead the next day.

"She went in and saw blood in the living room and then found her aunt laying in the bedroom on her bed in an awkward manner," says Assistant Burleigh County State's Attorney, Pam Nesvig.

Dean Grenstiner walked into court Tuesday smiling.

Even smiling several times during the hearing where he pleaded guilty to murder for the death of his mother...

Nesvig says Ann Grenstiner's autopsy shows her cause of death to be from blunt head injury due to multiple impacts to her head and face. The impact injuries to her face and scalp were associated with lethal injuries to the brain. Impact bruises similar to pattern of a shoe. The additional bruises on arms and shoulders consistent to her raising her arms in protective gestures at the time of the injuries.

Nesvig says evidence showed Grenstiner tried to clean up the bloody mess left behind in the brutal killing.

"It appeared somebody had cleaned the carpet, even cleaned the carpet, some blood splatter on the walls, cleaned up as well. Washing machine, recently laundered items, trap showed there had been blood. Along with blood in the sink," says Nesvig.

Investigators were told of a tumultuous relationship Grenstiner had with his mother...

Nesvig says not only did relatives have a hunch Grenstiner was the "suspect" but he also admitted to the crime during a recorded call he made from jail.

Nesvig says,"he indicated that after 27 years of having a difficult relationship with his mother that he decided it was time to end it. He specifically stated to this individual that he kicked his mother to her death, that she was breathing and snoring as he was doing so."

Grenstiner will be sentenced after an evaluation.

Grenstiner is also charged with theft of a motor vehicle, he pleaded not guilty to that crime.

As part of a plea agreement, the theft charge may be dropped when he is sentenced.

Prosecutors will not give details of the plea agreement.

Grenstiner faces life in prison without parole.