Cops: Son, 23, Drowns Own Mom in Backyard Pool They fought over his medication: prosecutor By Arden Dier, Newser Staff Posted Aug 19, 2016 12:05 PM CDT 168 comments Comments Denis Cullen (Suffolk County Police) (Newser) – In what authorities describe as a "chilling" case, New York police say a 23-year-old put his mother in a headlock and drowned her in the family's pool on Long Island on Wednesday. Assistant DA Robert Biancavilla says 63-year-old Elizabeth Cullen initially argued with her son, Denis Cullen, in the shallow end of the pool over whether Denis had taken his psychiatric medication. But when she poked him, per the AP, Denis dragged her into the deep end, "waited until she stopped moving, and then carried the body out of the pool," Biancavilla tells CBS New York. Biancavilla says Denis tried to hide the body before stealing his mom's car, cash, and credit card. He then traveled to his sister's house where he reportedly confessed. Police were called to the scene and found Elizabeth Cullen dead in the backyard. Biancavilla adds that Denis—previously diagnosed with paranoid schizophrenia, per WABC—later confessed. "He said she struggled violently and he was surprised a woman of her stature could struggle as much as she did," says Biancavilla, calling the description "chilling." Denis, who is the nephew of former US Army Chief of Staff George Casey, is charged with second-degree murder.