A 22-year-old Long Island man will spend decades behind bars for stabbing a 16-year-old high school student -- at the time, his classmate -- in the heart at a strip mall several years ago, killing him.

Tyler Flach, of Lido Beach, was sentenced Tuesday to 25 years to life in prison in the September 2019 stabbing death of Khaseen Morris, who was a 16-year-old recent transfer student to Oceanside High School at the time of his killing.

A jury convicted Flach on charges of murder, gang assault, assault and criminal possession of a weapon on the first day of November last year after a roughly two-week trial. They deliberated for about a week before reaching a verdict.

"Khaseen Morris was intelligent, friendly and had a smile that could light up a room," Nassau County District Attorney Anne Donnelly said in a statement Tuesday. "The young man was only 16 years of age and had recently transferred to a new high school, where he was making friends. The defendant, angry that Morris had walked a girl home, organized a group and went to a local strip mall with the intention of attacking Morris."

According to court records, Morris had only attended Oceanside High School for 10 days before he was killed on the afternoon of Sept. 16, 2019. Prosecutors say Flach and several other people got out of Flach's car on Brower Avenue in Oceanside shortly before 4 p.m. that day and set upon Morris, along with several of his friends. It was, officials have said, an apparent after-school fight over a girl that erupted outside a pizzeria in the shopping plaza that day.

At some point during the brawl that was captured on video and posted on social media, Flach stabbed Morris in the heart. The teen's heart stopped beating. Trauma doctors were able to revive Morris once he got to the hospital, but he died that September night. It was about eight hours after the stabbing.

"Tyler Flach stabbed Morris in the chest and took the young man’s life," Donnelly said. "This was an incredibly senseless murder...We continue to stand with Khaseen’s family, friends, and community as they mourn his tragic loss."

Flach surrendered to police two days after the incident. Most of the charges against him were related to Morris' death. He also was convicted of assault for breaking the arm of another teenager.

When asked outside of court on Tuesday if he regretted what happened, Flach said simply, "yes." Inside of court, Flach said in a statement "I hate that day, I hate myself...It’s hard for me to live knowing by my hands someone died." He also added "I did not try to kill anybody that day and I’m sorry. I’m sorry."

However, the judge was not convinced, saying that "As I see it, you were trying to impress people on your side of stupidity." Flach then interrupted, yelling "we were kids, we were kids...it was an accident."

Morris' family wore hearts on their jackets in court on Tuersday to show their how heartbroken they are over the loss of their loved one.

"Finally he was held accountable for what he did," said Heyanna Morris, the victim's sister, who also was not interested in hearing any of Flach's excuses or apologies he made before the court.

"He chose to get in that car, he chose to bring a knife, he chose to stab my brother — all of those were his decisions," she said. "So I refuse to entertain any sob story from Tyler."

One of Morris' sisters said to Tyler during the court proceeding "I hope you're proud of yourself" — to which Flach shook his head, indicating he was not.

Flach's family did not make any statements, but their attorney vowed to appeal.

"He's a young man and what he was trying to put forth is that he knows he made a mistake and that he wasn’t trying to impress anyone, and he certainly wasn’t trying to kill anyone," said defense attorney Kevin Dunshee.

As for the nature of the appeal, Dunshee alleged that evidence in the case may have been mishandled. The judge said that Flach would be spending his sentence in a Fishkill prison.

A co-defendant, Haakim Mechan, was sentenced last week to three years in prison with three years of post-release supervision after pleading guilty to second-degree attempted gang assault.