OCEANSIDE, N.Y. (CBSNewYork) – Police have made an arrest in the stabbing death of a teenager on Long Island.

Authorities say 18-year-old Tyler Flach of Lido Beach has now been charged with second-degree murder for the death of Khaseen Morris.

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Khaseen Morris, 16, was stabbed to death when a brawl broke out outside a strip mall on Long Island.

Disturbing video captured the deadly brawl outside a pizzeria in Oceanside Monday afternoon that led to the 16-year-old’s murder.

The senseless brawl was caught on cellphones by some of the 50 or more teens gathered at an Oceanside strip mall after school on Monday in what police said was a prearranged fistfight after Morris was seen with another boy’s girlfriend.

Police said Khaseen was threatened, then set upon by six or seven teens from another school district. He was stabbed once in the chest and later died.

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Detectives had a warning for witnesses that have not yet come forward.

“If you are not a part and parcel of murder of Khaseen Morris, now is the time to get in touch with us and let us know who did this and why,” Nassau County Police Det. Lt. Stephen Fitzpatrick said.

Flach is scheduled to appear in court on Thursday.

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