The video was shown Monday during a Family Court hearing to decide whether a 16-year-old girl charged in the death of Amy Joyner-Francis should be tried as an adult on charges of criminally negligent homicide and conspiracy.
The judge said he would rule by the end of next week after receiving final written submissions from attorneys.
The defendant is accused of repeatedly hitting Joyner-Francis in a premeditated attack April 21 at Wilmington's Howard High School of Technology. Two other girls are charged with conspiracy.
The Associated Press is not naming the defendants because they are juveniles.
The Division of Youth Rehabilitative Services and a clinical psychologist who testified Monday for the defense have recommended that the alleged assailant be tried in Family Court, meaning she could be sentenced to community supervision if found to be delinquent.
Psychologist Robin Belcher-Timme testified that the girl has responded well to counseling, has no prior criminal history or evidence of personality disorders and presents a low risk of future violence.
"We have an opportunity to intervene," he said. He acknowledged that the girl's school performance and attendance had declined in the past year and that some of her friends were delinquent, but he asserted that her issues amount to "correctible behavior."
Prosecutors are seeking to try the girl in Superior Court, where she faces up to eight years in prison if convicted. They note that she showed no remorse immediately after the fight or later, after learning that Joyner-Francis, whose fingernails were ripped out during the fight, had died.
"Somebody else must have kicked her. ... Well they're not going to put this on me," the girl said after learning of Joyner-Francis' death, according to deputy attorney general Theresa Sedivec.
A medical examiner said Joyner-Francis, 16, had a pre-existing heart condition, but that she was a victim of homicide. Authorities say she suffered sudden cardiac death, with a contributing factor of physical and emotional stress due to physical assault.
In a police affidavit, investigators said the defendants planned the attack over a 20-hour period.
Wilmington police detective Thomas Curley testified that in an online group chat the day before the attack, Joyner-Francis offered advice to one of her friends about a problem involving a boy, telling her friend to "just be careful." Curley said the defendants were later brought into the chat, and that the alleged attacker thought Joyner-Francis was talking about her.
Prosecutors played a recording made by a friend of Joyner-Francis of a Snapchat posting by one of the defendants the day before the fight. The post shows Amy trying to talk to her alleged assailant in what Curley was told was an attempt to defuse the situation. The posting also includes a message noting that the girl charged with homicide was "bouta fight her," followed by several emojis indicating that a person was laughing so hard she was crying.
In the posting, the defendants can also be heard reportedly saying, "She's scared. She's scared. We gonna get her."
Curley also testified that one of the defendants said in an online post the next day that she was told to wear her sneakers, indicating that there was going to be a fight. Joyner-Francis was wearing sandals on the day of the attack, he said.
Curley said a math teacher who responded to the disturbance in the bathroom saw the defendants laughing and giggling as they left. He said the teacher found Joyner-Francis sitting on the floor, trying to prop herself up with her hands before she uttered her last words.
"They jumped me. They snuck me," she told the teacher, according to Curley.