TULSA, Okla. (AP) — Two Tulsa children whose bodies were found in waterways in May accidentally drowned, the Oklahoma medical examiner’s office ruled Friday.

Autopsy reports say both 3-year-old Miracle Crook and her 21-month-old brother, Tony Crook, drowned after being last seen on video holding hands and walking through an opening in a chain-link fence toward a rain-swollen creek that flows into the Arkansas River.

Miracle’s body was found in the river while Tony’s body was found in the creek.

Their mother, Donisha Willis, 24, was arrested at the time on charges of child neglect and assaulting a police officer.

The neglect charges have since been upgraded to second-degree murder, and Willis has pleaded not guilty. She remains jailed on $500,000 bond, according to jail records.

Police have said Willis, who did not have custody of the children, broke into an apartment where the children were with a caretaker. The caretaker left the apartment and later returned with the legal guardian to find Willis passed out on a couch and the children missing.