Man Accused of Dragging Mother Into Swimming Pool, Where He Drowned Her

After the unthinkable act, police say Denis Dyson Cullen took a train to his sister's home to confess.

Police say a 23-year-old New York man drowned his own mother in the deep end of the family's swimming pool.

Denis Dyson Cullen allegedly put his 63-year-old mother Elizabeth into a headlock before dragging her from the shower to the pool on their palatial multi-million dollar estate on Long Island and held her under.

Read: Man Perishes on Family Farm After Manure Fumes Form 'Deadly Dome of Air'

Cullen was arrested Wednesday night at the family’s Lloyd Harbor home, which is located in an exclusive enclave of multi-million-dollar properties.

Cullen has a history of drug addiction and mental problems. Prosecutor Robert Biancavilla said he fought with his mom because he had stopped taking his medication.

“The argument escalated to the point where she had poked him,” Biancavilla said Thursday morning. “After she poked him, he put her in a headlock, walked her from the shallow end of the pool to the deep end of the pool, all the while she struggled. He said she struggled violently and he was surprised a woman of her stature could struggle as much as she did.”

After the murder, Cullen took a train to New York City to meet one of his sisters and confessed everything, according to authorities.

Police received a call Wednesday afternoon about reports of an intentional drowning. As both local and county police were inspecting the property, Cullen returned home.

Family sources say that Elizabeth Cullen had three daughters and was overjoyed when she finally had a son she desperately wanted. No one could have imagined that 23 years later, her son would be accused of such an unthinkable murder.

The accused killer is the nephew of George Casey Jr., the former U.S. Army Chief Staff Coalition Commander in Iraq under President George W. Bush.

His father, also named Dennis, is a wealthy investment banker and a member of one of America’s most exclusive golf clubs, The Creek.

Family photos show the Cullens on vacation in Spain in 2013 in much happier times.

Cullen pled not guilty to second-degree murder when he was arraigned and ordered held on $5 million bail.
Police say he confessed in "chilling detail" to the crime.

“This is a son who killed his mother, and the way he killed her, the way he describes, how it was done, is chilling,” Biancavilla said.

Defense attorney Steve Fondulis has been assigned Cullen as a client. Newsday reports that he only spoke to his client for 10 minutes.

Read: Dad Who Killed His 11-Year-Old Daughter Asks God for Forgiveness at Her Funeral

There’s a lot of work to be done,” Fondulis said. “I have to determine if he had a psychiatric background. I have to determine if he’s under a doctor’s care. And I have to look at a videotape.”

He added: “He’s not sorry at this point; he hasn’t said I’m sorry.

No other family members were home at the time of the incident. His sisters all live outside of the home.

Watch: 20 Years After JonBenet Ramsey's Murder, Where is Her Family Today?