(CNN) An 11-month-old baby in Tennessee died after his mother left him in a bathtub with his sister Wednesday, the Knox County Sheriff's Office said.

Lindsee Leonardo has been charged with first-degree murder and aggravated child abuse after she left her baby, Aidan Xavier Leonardo, and his 2-year-old sister in a tub in about 4-6 inches of water, according to the sheriff's office.

CNN has reached out to Leonardo's lawyer, Susan Shipley, for comment.

According to a police affidavit, Leonardo told deputies she went outside for about 10 minutes to "smoke a cigarette and have some 'me time.'" After listening to music, she went back inside and found the baby floating on his back while his sister stood in the water, she said.

Leonardo said the 2-year-old had turned on the water and filled the tub to the top, according to the affidavit.

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