Police revealed that a 16-year-old girl who died after a school bathroom fight had a pre-existing heart condition

A 16-year-old girl died after a fight broke out in the girls' bathroom at a Delaware high school, and authorities have now revealed she died of sudden cardiac death, ABC News reported.

Amy Inita Joyner-Francis, a sophomore at the Howard High School of Technology in Wilmington, Delaware, had a pre-existing heart condition, and the stress of the assault contributed to her death, according to authorities.

After her death, cell phone video of the altercation emerged, showing Joyner-Francis down on her knees being punched, according to CBS News.

John Deckers, an attorney for one of the 16-year-olds involved in the fight, has said that his client could not have known her actions would result in death.

Deckers' client is being charged with criminally negligent homicide and is accused of hitting Joyner-Francis repeatedly in the head and torso. Prosecutors are aiming to try her as an adult. She is currently under home confinement, according to ABC.

"The altercation was between two teens who knowingly and willingly entered the bathroom for that purpose," he said in a statement to the Associated Press, according to ABC.

"The possible consequence - that a consensual fight, involving no blunt force injuries, could ever result in death due to an unknown, pre-existing medical condition - was entirely unapparent to either girl."

A statement from the school indicated that a "physical altercation" began in the girls' bathroom at 8:15 am on Thursday, April 21.

"She was fighting a girl, and then that's when all these other girls started banking her - like, jumping her - and she hit her head on the sink," Kayla Wilson, a Howard High student in a bathroom stall when the fight broke out, told a local TV station, according to The Associated Press.

Joyner-Francis was then airlifted by helicopter to the Nemours/Alfred I. duPont Hospital for Children, where she later died.

The two other female student involved in the fight are being charged with misdemeanor conspiracy.

Howard High and the surrounding community are mourning Joyner-Francis' death. A memorial page on Facebook was set up for Joyner-Francis, and on Twitter the hashtag "#RIPAmy" began to circulate.

"My heart bleeds for the family," Wilmington Mayor Dennis P. Williams said at a press conference. "Things like this shouldn't happen."