A 21-year-old Dix Hills man with a history of mental problems was sentenced Friday to 30 to 40 years in prison for the choking death of his 15-year-old brother and the brutal beating of his mother during a family argument in 2014.

State Supreme Court Justice Mark Cohen imposed the maximum sentence on Charles Okonkwo Jr., despite pleas from the man’s father that his son get a lesser sentence and psychiatric treatment while he is in prison.

“He is the only thing I have left,” Charles Okonkwo Sr. said during the sentencing proceeding in Riverhead as his injured wife sat in a wheelchair in the courtroom. “I’ll be dead probably before he comes out.”

Before and after the court session, the Okonkwo family huddled with defense attorney Eric Besso of Sayville, not with the prosecutor, as is typical for families of victims.

Outside court, prosecutor Glenn Kurtzrock shook his head. “This is case where the victim’s family is also the defendant’s family,” he said.

Both prosecutors and the defense said Okonkwo Jr. had a history of mental problems.

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The defendant, who had waived his right to present a psychiatric defense, was convicted of manslaughter last month in the choking death of his brother, Bradley, and first-degree assault for the beating of his mother, Chinwe Okonkwo, who is still undergoing treatment. The mother, a medical doctor, did not speak in court and did not respond to reporters’ questions outside court.

The defendant appeared in court in handcuffs that were secured in front to a belt around his waist — a security precaution taken since he was accused of assaulting a correction officer while in jail. That incident took place in July 2014, according to online court records, and the case is pending.

“I’m sorry for what I’ve done,” the younger Okonkwo told the judge Friday. “I had no intention of hurting my family.”

Kurtzrock had urged the maximum sentence because of what he said was Okonkwo’s history of violence.

“Hopefully, the defendant will get the help that he needs and while he’s getting the help that he needs, we’re going to be protected,” he said later.

In court, the prosecutor acknowledged Okonkwo’s psychiatric history, but said Okonkwo knew his actions were wrong.

Kurtzrock said during the 10-day trial that Okonkwo, 19 at the time, choked his brother for several minutes until he died, and that he repeatedly hit his mother, putting her in a coma.

Before imposing the sentence, the judge spoke directly to both father and son.

“You will have to live with the fact that you are your brother’s killer,” he told the son.

Turning to the father, the judge said: “I’m a father and a grandfather. I understand the heartbreak that this entails.”

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Okonkwo will have to serve a minimum of 30 years before becoming eligible for parole. He will be on post-release supervision for an additional five years at the end of the 40-year period.