A Washington woman faces charges of assault and unlawful imprisonment after investigators said she tied her 80-year-old mother to a chair and tried to strangle her.

According to a probable cause affidavit filed in Pierce County Superior Court, Leisa Wagner, 50, became frustrated with her mother because she had to help her use the bathroom too many times a day. Police said the elderly woman suffers from dementia.

Wagner is accused of tying up her mother Thursday night and wrapping a sheet around her neck as the elderly woman screamed for help.

“Our officers arrived, found the elderly female still sitting in the chair tied with the bedsheet,” said Puyallup police Capt. Scott Engle.

Police say the incident was witnessed by another family member, who recorded part of it on cellphone video.

Investigators said the family member told them he heard Wagner shouting, “You need to stop going to the bathroom every five seconds. If you don't stop giving me a hard time, I will tie you up and lock you in here and never let you out."

Police said the witness called 911 for help, and Wagner was arrested.

Investigators said that because of the woman’s dementia, the cellphone video will play a key role in the case, giving them evidence the victim may not be able to supply because of her medical condition.

“Many times, they are not able to speak with us coherently because of the dementia,” said Engle. “So this time, having that video shows us exactly what happened. A picture paints a thousand words.”

Wagner pleaded not guilty to the charges during her arraignment on Friday. She was freed without bail.