The family of a teenager slain in a Hempstead machete attack struggled to stay composed Friday as his killer spoke in court and offered what a judge called “excuses” that didn’t justify the deadly violence.

“When you take a machete, which as you know and everybody in the courtroom knows, is a very big knife, and you swing it as hard as you can at somebody, what do you think is going to happen?” acting State Supreme Court Justice Patricia Harrington asked David Sadler in Nassau County Court. “I’m flabbergasted to continue to hear your excuses.”

Harrington then sentenced Sadler, 47, who had been a well-known pizza deliveryman in Hempstead, to a maximum 25 years in prison for first-degree manslaughter in the 2014 death of Terrence “T.J.” Grier Jr.

StoryMan found guilty in machete attack that killed teenDataLI crime stats

The judge told Sadler, who also was convicted on a weapon charge, that his actions “took the life of a 17-year-old boy who had his whole future ahead of him.”

She added: “Even if they did what you say they did . . . there is no excuse for what you did — none, absolutely none.”

Sadler had claimed Grier was among a group of people who beat and robbed him on July 18, 2014, after a dice game. He claimed Grier stole money from his pockets and a struggle ensued before he swung the machete in self-defense.

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The blade severed a carotid artery and a jugular vein in the teenager’s neck, prosecutor Martin Meaney said in court Friday, calling Sadler’s action a “heinous and horrific act.”

Meaney said during the February trial that Sadler had been playing dice on a Hempstead street with Grier and others, and an argument got physical after Sadler lost his money.

Sadler went and got a machete and Grier told him to “drop the knife” if he wanted to fight, the prosecutor said. But Sadler instead inflicted a gaping neck wound and first-aid efforts weren’t enough to save him, Meaney said.

Sadler offered condolences and apologies to Grier’s family Friday, but insisted he had been “beat up and robbed” that day.

“I’ve never denied my actions. I’ve only tried to explain why it happened,” he said.

But Greta Price, 48, of Hempstead, the victim’s mother, couldn’t bear to listen to Sadler.

“Does he have to keep talking?” she whispered to a court officer, before leaving the courtroom and breaking down in tears in the hall.

Grier’s father, Terrence Grier Sr., 51, interjected as Sadler spoke, asking why he didn’t call the police if he had been victimized.

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After Harrington restored order to the court, Sadler attacked the victim’s character before ending his minutes-long remarks by saying what happened “was a reaction and I’m human.”

“It doesn’t change it, but I’m sorry,” he added.

Defense attorney Brian Carmody of Westbury declined to comment after the sentencing.

Price said later that the family was relieved her son’s killer got the top punishment and that she still struggles to wake up in the morning, knowing her son is dead.

The victim’s father said Sadler’s words frustrated him.

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“He had ample time to call the police but . . . he did what he did, so he deserves to do the time. . . . We have to go on with life, but still my son is not here.”