A 30-year-old Arizona man was arrested after police said he killed his grandmother because he was tired of caring for her. 

Officers arrived at an apartment complex in Chandler early Sunday morning and found 81-year-old Helen Smith dead. Her grandson, Brandon Smith, was later arrested and charged with first-degree in connection with her death. 

According to Chandler police, Brandon was frustrated that he was the only one in the family taking care of Helen, who suffered from dementia.

Helen had urinated on herself so Brandon took her to the bathroom for a shower. That's when he slapped her in the face and she fell unconscious in the tub, police said.

He then told police he decided he didn't want his grandmother to "live like this anymore" and wanted to kill her, according to court documents. So he went into the kitchen, grabbed a knife and cut her throat, police said.

“I could not imagine, I could feel her feeling, walking in, seeing your mom dead,” said tearful Marca Whitehair, who lives in the apartment below the victim. She said she and her family heard the cries for help from other family members when they found their loved one dead.

"She was screaming, she was frightened," said Whitehair. "She just kept yelling, like, 'Grandma's gone, grandma's gone!'” 

"Nothing like this has ever happened! I came out and there were about 20 officers, 20 cops cars around the building,” said Alan Blanchard.

Brandon was already on probation for aggravated assault, according to police.

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