The teenager arrested in connection with the fatal stabbing of a high school student on Long Island was ordered held without bail Thursday at his arraignment on a second-degree murder charge.

Tyler Flach, 18, of Lido Beach, was arrested Wednesday in the death of 16-year-old Khaseen Morris. He pleaded not guilty at his arraignment.

Tyler Flach. Nassau County Police Department

Morris was stabbed in the chest during a large brawl among teens Monday in a strip mall parking lot in Oceanside, a Long Island community about 30 miles east of Manhattan, authorities said. The fracas was precipitated by a dispute over a girl, according to police.

Morris' family moved to Oceanside this summer from Freeport, a neighboring town on the South Shore of Long Island.

Officials said that most of the 50 or so teens who either took part in or witnessed the attack, instead of coming to Morris' aid, recorded cellphone video of the fight. Some of that video was posted on social media.

“Kids stood here and didn’t help Khaseen,” Nassau County Det. Lt. Stephen Fitzpatrick said earlier this week. “They’d rather video. They videoed his death instead of helping him.”

Edward Sapone, Flach's Manhattan-based attorney, told NBC News after the arraignment that his client strongly maintains his innocence.

"This is a very sad time for the victim's family and our hearts go out to them," Sapone said. "We have commenced an in-depth defense investigation that has already revealed important details which we will release at the appropriate time."

The judge granted Sapone's request that Flach be held in protective custody.

"I made an application that the judge place him in protective custody because there is evidence that the victim's group has strong ties to the Bloods violent street gang," Sapone said. "The Bloods are threatening to kill Tyler, they're threatening to get him in the correctional facility and they're threatening to retaliate against him."

Flach is due back in court on Monday.