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(CNN) —  

The California teen accused of murdering an Italian police officer in Rome had been previously charged over an assault in the United States, according to a source with knowledge of the events following the incident.

The source said Finnegan Lee Elder, 19, was charged over a 2016 assault of a high school classmate that resulted in severe injury. The details of the assault and Elder’s involvement, which took place on October 29, 2016 in San Francisco, were first reported by the San Francisco Chronicle Tuesday.

Elder, who was 16 at the time, struck a fellow student and football teammate from the Sacred Heart Preparatory school in San Francisco resulting in the victim hitting his head on the pavement, the source told CNN. It’s unclear what, if any, punishment Elder received.

Elder, left and Hjorth, right, were arrested in their hotel room in Rome last Friday.
Elder, left and Hjorth, right, were arrested in their hotel room in Rome last Friday.
PHOTO: Italian Carabinieri via AP

Elder and a fellow American Gabriel Natale Hjorth, 18, were arrested last Friday in their room at Rome’s Le Méridien Visconti hotel. They are accused by Italian police of killing a Carabinieri officer, Mario Cerciello Rega, earlier that day.

Rega, who was unarmed and in plainclothes, was attacked while attempting to recover a backpack allegedly stolen by Elder and Hjorth after a botched drug deal, police say.

While both teens admitted to the assault, according to police, only Elder is accused of stabbing Rega 11 times with a seven-inch knife which officers say he brought from the US to Italy.

Hjorth’s father said Wednesday his son was “distraught” by what happened but is innocent of the officer’s death. Fabrizio Natale told CNN Natale Hjorth did not know Elder was armed and only became aware of what actually happened after his arrest.

He said he visited his son in an Italian detention facility on Wednesday morning, describing the encounter as “very emotional” and “very hard.”

“He’s devastated by the Carabinieri’s death. And I, for one, as a father painfully feel this family’s grief,” Natale said.

’Put into a coma’

The Chronicle reported Wednesday that back in 2016 Elder punched a fellow member of his high school football team at a night-time gathering of students.

The San Francisco District Attorney’s office would not comment on the case as it involved a minor and the juvenile records are sealed. The San Francisco Police did not immediately comment.

Caleb Lagafua, who played on the football team with Elder at the time, told CNN that he was not present that night. But he remembered the fallout from the incident.

“I remember the kid he punched … got put into a coma … and then the parents were pressing charges. The kid didn’t come back I think until the last few months of school,” he said.

Lagafua, who is now attending college in San Francisco, said Elder told him about the incident afterwards.

“I remember Finn tried to tell me the whole story. 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 said he was friendly with Elder, but tried to keep his distance from his teammate. He remembers Elder getting into fights with teammates during football practice. “It was over stupid stuff,” Lagafua said.

“He was always running with like some bad kids and I didn’t want to mess up my future being around that. But I do remember the fight because it happened over a weekend and I just remember I came back to school and everyone was talking about that Finn was in jail … it was crazy cause I didn’t think anything like that would happen at Sacred Heart. I just know that Finn had a lot of anger in him.”

An image of the knife  Elder is alleged to have brought from the US to Italy was displayed prior to a press conference in Rome on Tuesday.
An image of the knife Elder is alleged to have brought from the US to Italy was displayed prior to a press conference in Rome on Tuesday.
PHOTO: FILIPPO MONTEFORTE/AFP/AFP/Getty Images

Immediately following the incident, the Chronicle published a news story, citing a San Francisco police spokeswoman, reporting that the victim was hospitalized with “life-threatening injuries” and that Elder turned himself in and was booked with juvenile authorities on suspicion of battery involving serious bodily injury.

The Elder family had no immediate comment but family spokesman and Finnegan Elder’s uncle Sean Elder told the Chronicle that the 2016 incident was part “a mutual pre-agreed upon fight, which many football team members knew about and egged on.”

“I’ve known Finn for his entire life and have never seen him be violent, or even lose his temper,” Sean Elder told the Chronicle.

He added that Finnegan received no disciplinary action from the school.

Forensic analysis

Slain Italian police officer Mario Cerciello Rega with his wife on his wedding day.
Slain Italian police officer Mario Cerciello Rega with his wife on his wedding day.
PHOTO: Facebook/Rosa Maria Esilio

Italian investigators were carrying out forensic analysis on their hotel room on Wednesday, Italian police confirmed to CNN.

Police images of their arrest show Elder with a partially missing middle finger. His mother Leah Elder told CNN Tuesday that her son fell off a ladder in an industrial accident a few years ago, leaving his left hand partially paralyzed and his finger amputated.

“He was hospitalized for days while they attempted reattachment surgery of the finger twice and then it didn’t take and he had to have amputation surgery,” she said.

Arrest and court documents do not mention this physical detail.