More details have emerged from acquaintances and family members about Finnegan Elder, the 19-year-old who's accused in the killing of a 35-year-old Italian police officer last Friday. And it sounds like he has a history of courting violence.

Elder attended Sacred Heart Cathedral Preparatory in San Francisco prior to moving on to Tamalpais High in Marin — where he and the friend who's also been implicated in the slaying, Gabriel Natale-Hjorth, graduated in 2018. And as his uncle, Sean Elder, tells the Associated Press, Elder attended "fight nights" in a local park that "apparently resulted in many injuries."

One of these nights may have been the venue for an incident that the Chronicle reported on Tuesday: Elder was implicated in an incident at "a 2016 late-night party in Stern Grove" that left a fellow Sacred Heart student with a severe brain injury. Though the records of the incident were sealed because Elder was a juvenile at the time, sources familiar with the investigation told the Chronicle that Elder was arrested on suspicion of battery involving serious bodily injury, and was found guilty in juvenile court. Details of his sentence, or any further disciplinary action taken by Sacred Heart, are not known.

The Chronicle covered the October 2016 incident at the time, reporting that "the boy who allegedly caused the injuries later turned himself in."

Caleb Lagafua, a fellow football player at Sacred Heart, tells KPIX that the victim was "put into a coma," and kids came to school afterwards hearing that "Finn," as they called Elder, was in jail.

"I remember Finn tried to tell me the whole story" Lagafua tells the station. "He told me that it wasn’t his initial contact that put him in a coma. He said that after he punched him, he fell and he hit his head on the rock."

Lagafua says he didn't run with the same "bad kids" as Finn, and adds "I just know that Finn had a lot of anger in him."

Sean Elder, the uncle who is acting as the family's spokesperson, issued a statement, per the Chronicle, saying, "I've known Finn for his entire life and have never seen him be violent, or even lose his temper." And he again clarified to the Chronicle that the 2016 incident stemmed from a "a mutual pre-agreed upon fight, which many football team members knew about and egged on." He also says that Elder did not transfer to Tamalpais High because of any disciplinary action — only because his father moved to Mill Valley.

The victim in the 2016 punching incident apparently recovered from his injuries after a long process, and ultimately finished high school and went on to college. The Chronicle did not reach him for comment.

Elder has said that he stabbed the unarmed Italian Carabinieri officer, Mario Cerciello Rega, in self-defense. He claims the officer was attempting to restrain him by the neck, though a judge said there were no obvious marks of strangulation on Elder's neck. Rega was stabbed 11 times.

Observers have noted that Elder's middle finger appeared to have been amputated in the photo seen below from Italian authorities (left). Elder's mother tells CNN that was the result of an "industrial accident" several years ago, which also left his hand partially paralyzed.

Related: 19-Year-Old Bay Area Man Jailed In Italy For Cop Killing Claims Self-Defense