WILMINGTON, Del. (AP) — Was the death of a 16-year-old girl the predictable result of a school bathroom fight that amounts to homicide or a tragic, unforeseeable circumstance resulting from her undiagnosed heart condition?

A Delaware judge will answer that question Thursday in deciding whether three teenage girls are culpable for the death of fellow student Amy Joyner-Francis.

The girls, all 17, were tried as juveniles after the April 2016 fight at Howard High School of Technology in Wilmington.

An autopsy found that Joyner-Francis, who had a rare and undiagnosed heart condition, died of sudden cardiac death aggravated by physical and emotional stress from the fight.

Her alleged assailant is charged with criminally negligent homicide, a felony. All three girls, who were 16 at the time of the fight, are charged with misdemeanor conspiracy. The Associated Press is not naming them because they are minors.

Defense attorneys argued that Joyner-Francis was a willing participant in a fight between mutual combatants and that her death was unforeseeable.

Prosecutors contend that Joyner-Francis wasn't looking to fight and was unexpectedly attacked while trying to defuse a tense situation caused by confusion over an online group chat.

The judge, presiding over a non-jury trial, must decide whether the conduct of the alleged assailant and her failure to perceive the risk that Joyner-Francis might die was a gross deviation from a reasonable person's standard of conduct.

Dr. Richard Ringel, a pediatric cardiologist and professor at Johns Hopkins University, testified that Joyner-Francis had Eisenmenger syndrome, an extremely rare condition for someone her age in which a heart defect combines with severe pulmonary hypertension.

Prosecutors say that in an online group chat the day before the attack, Joyner-Francis offered advice to a friend about a problem involving a boy, telling her to "just be careful." A detective testified that the defendants were later brought into the chat, and that the alleged attacker thought Joyner-Francis — who had warned that someone might betray another person — was talking about her.

A Snapchat posting by one of the defendants that same day shows Joyner-Francis talking to her alleged assailant in the bathroom, purportedly to try to defuse the situation. The posting notes that the girl later charged with homicide was "bouta fight her," followed by several emojis indicating that a person was laughing so hard she was crying.