When a Freeport Village police officer arrived at the scene of a brawl in the winter of 2014, he saw a wounded teenage girl lying on the sidewalk in a residential neighborhood.

The girl, Abbigale Thomas, 17, was gasping for air, said the officer, John Florio, the first witness to testify Monday at the trial of Jasmine Copeland, who authorities said fatally stabbed Thomas in the back with a steak knife on Nov. 1, 2014.

“She was gargling. She couldn’t speak,” Florio told jurors in Mineola. “There was blood coming out of the puncture wound, as well as air bubbles.”

Thomas, whose lung was pierced during the attack, “drowned in her own blood,” Nassau Assistant District Attorney Ali Ajamu said Monday during his opening statement before state Court of Claims Judge Alan L. Honorof in Nassau County Court.

Copeland, 18, a senior at Freeport High School, is charged with manslaughter and other crimes in Thomas’ death. Copeland has pleaded not guilty.

Trouble began when Copeland and one of Thomas’ foster sisters, Nubian Middleton, had a falling out, and the girls traded insults on Facebook and via text messages, Ajamu said.

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The slights, “you’re fat” and “you’re ugly”, were the usual kind of hurtful comments some kids flung at each other, Ajamu said. But he said the verbal abuse escalated when Thomas, her foster sisters, Nubian Middleton and Diamonique Middleton, and the Middletons’ cousin, Miracle Nixon, walked several blocks to Copeland’s house looking for a fight. The girls, however, did not bring along weapons.

“That all changed when the defendant brought a knife to the fight,” Ajamu told jurors.

Copeland, who was at her friends’ house two doors away, grabbed a steak knife from their kitchen, and she and the three friends, all sisters — Janelle Walker, Janae Walker, and Amanda Walker — went outside and words were exchanged, said Ajamu.

Thomas struck Copeland and a brawl broke out, Ajamu said. While Thomas was on top of Janelle Walker, beating her, he said Copeland stabbed Thomas in the back.

“Abbigale Thomas never saw it coming,” Ajamu said.

Immediately after the stabbing, Ajamu said Copeland confessed to Janelle Walker.

“Please don’t let her die, the defendant said,” Ajamu told jurors. “Please don’t let her die.”

Police recovered a silver knife from the kitchen of the Copeland house with reddish residue that Nassau Homicide Det. James Cereghino testified he thought was blood. The knife, which he said did not match the utensils in the Copeland house, was analyzed, but did not contain blood or genetic material.

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Ikiesha Al-Shabaz, Copeland’s attorney, said her client brought a knife to the fight, but did not use it to stab Thomas. If Copeland had, Al-Shabazz said, Thomas’ blood would have been on Copeland’s clothes.

“She dropped the knife that she had,” Al-Shabazz said during her opening statement.

Copeland fought Diamonique Middleton, who Al-Shabazz said was twice Copeland’s size, and used both hands to pull the girl’s hair extensions. Police recovered several pieces at the scene.

The only person who fought Thomas that night, Al-Shabazz said, was Janelle Walker, a cooperating witness who is scheduled to testify against Copeland in exchange for leniency.

“She [Janelle Walker] has every incentive to tell you a lie,” Al-Shabazz told jurors.

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The trial resumes Tuesday.