A Long Island man has been accused of murder after telling police that he killed his mother at their North Shore home. Denis Cullen was arrested Wednesday evening after allegedly drowning his 63-year-old mother, Elizabeth Cullen, in the family pool.

According to NBC New York, the 23-year-old man became a suspect in his mother’s death as investigators searched for clues. The police initially received a call reporting a possible intentional drowning around 3:45 p.m. Wednesday and discovered the victim’s body at the White Hill Road home, according to Newsday.

"The evidence suggests that she was intentionally drowned as the call indicated. While we were processing the scene, the suspect returned to the home and we placed him under arrest," Suffolk County Police Commissioner Timothy Sini told the media.

Denis Cullen returned home around 5:50 p.m. that same day and was arrested without incident. Sini would not comment on the suspect’s motive for murder nor his mental state. He was then processed on Thursday and stayed overnight at a precinct.

The Daily Mail reported that Elizabeth Cullen was a married mother of five whose brother is the former Army Chief Of Staff, George Casey. Her father reportedly was Major General George William Casey, the highest ranking officer killed in the Vietnam War. The victim was an account coordinator with advertising agency Edwin Bird during the 1980s and is believed to have owned an interior design company in Cold Springs Harbor.

Charged with second degree murder for his mother’s death, Denis Cullen pleaded not guilty during his arraignment. He has no criminal background and cash bail was set for $5 million on Thursday morning.