The Delaware Supreme Court on Thursday overturned a Family Court verdict that found a high school girl culpable of criminally negligent homicide in a beating that left her 16-year-old classmate dead.

All five justices ruled that Trinity Carr could not be blamed for the death of Amy Inita Joyner-Francis, who went into cardiac arrest and died of a rare and undiagnosed heart condition shortly after the attack in a Howard High School of Technology bathroom.

Though the condition was aggravated by the physical and emotional stress of the fight, the high court ruled that Carr, who was 16 years old at the time, never could have predicted that her assault would have caused the young student to die in the way she did.

“A defendant cannot be held responsible for criminally negligent homicide unless there was a risk of death of such a nature and degree that her failure to see it was a gross deviation from what a reasonable person would have understood, and no reasonable factfinder could conclude that [Carr's] attack—which inflicted only minor physical injuries—posed a risk of death so great that [Carr] was grossly deviant for not recognizing it,” Justice Gary F. Traynor wrote in a 30-page opinion.

Carl Kanefsky, a spokesman for the Delaware Department of Justice, said prosecutors were disappointed but respect the court's decision.

Traynor's opinion referred to Carr and Joyner-Francis by the pseudonyms Tracy Cannon and Alcee Johnson-Franklin because both were minors when the incident occurred.

A Family Court judge last June sentenced Carr to six months in a juvenile facility after finding her delinquent of criminally negligent homicide and conspiracy in the third degree.

According to Traynor's opinion, much of the state's case centered on cellphone video of the “one-sided” attack. In it, Carr is seen pulling Joyner-Francis by the hair and striking her with loosely balled fists. Prosecutors also pointed to a video posted to social media before the attack that showed Carr bragging about how she and other students were going to “get” Joyner-Francis.

The state medical examiner later found few outside signs of trauma, but discovered that Joyner-Francis died of a condition known as Eisenmenger syndrome, an atrial septal defect coupled with pulmonary hypertension, which is so rare that one study found it affects only 2.2 out of every 1 million children. The “emotional and physical stress” from the assault was found to be a “contributing” cause of death.

After a bench trial, Family Court Judge Robert Coonin found that Carr should have known that the assault posed an obvious risk of death and that there was a close link between that risk and the way Joyner-Francis had died.

“The natural and probable consequence of a physical attack on an individual is physical and emotional trauma which may, depending on the particular circumstances of the victim, result in varying degrees of physical harm, up to in its most severe degree, the death of the victim,” he said, according to Traynor's opinion.

“In this case, the evidence establishes beyond a reasonable doubt that the death of [Joyner-Francis] was caused by the action of [Carr].”

Carr appealed, arguing that she never could have foreseen that her attack would cause a teenage girl to die from cardiac arrest. Carr's attorneys also faulted Coonin for not analyzing the case under a provision of Delaware's Criminal Code, which requires a judge to evaluate the connection between the potential risks created by defendant's actions and the actual harm that occurred.

In conducting that analysis, Traynor found that the evidence precluded a finding of negligent causation beyond a reasonable doubt.

“But given the statistical improbability that a 16-year-old like [Joyner-Francis] might suffer from a rare, undiagnosed heart condition that would leave her mortally vulnerable to the type of assault that occurred in this case, we can reach only one conclusion in this case: even reviewing the evidence in the light most favorable to the prosecution, this essential element could not be proven beyond a reasonable doubt,” he wrote.

In a brief concurring opinion, Justice James T. Vaughn Jr. agreed with the court's ruling that Carr was not criminally negligent, but he said the causation analysis was unnecessary in Carr's case.

“In my view, stated simply, that section comes into play when the actor's state of mind satisfies the definition of criminal negligence, but the person injured is not the probable person or the actual injury is not the probable injury,” he said.

Carr was represented on appeal by Garrett B. Moritz of Ross Aronstam & Moritz and John P. Deckers of The Law Offices of John P. Deckers.

Carolyn S. Hake, deputy attorney general at the DOJ, argued for the state.

The case before the Supreme Court was captioned Cannon v. State.