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Isaias Plaza left the dock after his arraignment on Tuesday on the charges of manslaughter and assault and battery causing serious injury.
Isaias Plaza left the dock after his arraignment on Tuesday on the charges of manslaughter and assault and battery causing serious injury.Pat Greenhouse/Globe Staff/Globe Staff

WOBURN — One year later, the death of 15-year-old Richelle Robinson still perplexes and shocks. A powerful shove from an apparent assailant left the Cambridge Rindge and Latin School student fatally injured, unconscious, and bleeding on a busy sidewalk.

On Tuesday, an East Boston man was arraigned on charges of manslaughter and assault and battery causing serious bodily injury, stemming from the alleged attack. Prosecutors said discord among a group of teenagers led Isaias Santos Plaza to push Robinson hard onto the pavement July 22, 2018, along Cambridge Street.

Plaza, 19, remained out of view during most of his arraignment in Middlesex Superior Court. A not guilty plea was entered on behalf of Plaza, who was indicted by a grand jury Monday. He was held without bail at arraignment, and his court-appointed lawyer had no comment.

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As several of Robinson’s relatives looked on, wearing buttons that displayed her photo, Assistant Middlesex District Attorney Nicole Allain told the court that Plaza had socialized with Robinson and some of her friends in June and July 2018.

But eventually, Allain said, “discord” among the group caused Plaza and his then-girlfriend to split away from Robinson and two of her friends.

Allain didn’t elaborate on the conflict, which allegedly came to a head during the deadly encounter in front of Portugalia Restaurant.

Police were called to the area around 6:43 p.m. after receiving 911 calls regarding a young female lying on the ground, according to prosecutors. Officers saw Robinson with “blood coming from her nose and the back of her head,” said the government’s statement of the case filed in court. “She was unresponsive, did not have a pulse, did not appear to be breathing and her eyes were rolled back in her head.”

Robinson was later pronounced dead at Massachusetts General Hospital, records show, and the cause of death was determined to be “blunt force head injuries.”

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A witness indicated that a suspect, later identified as Plaza, had “forcefully” shoved Robinson with two hands, the statement said. The assailant was wearing a hoodie with the hood up, along with dark jeans and dark sneakers with white soles.

After allegedly shoving Robinson, the filing said, Plaza got on a bicycle and rode toward Boston. A McDonald’s cup at the crime scene and video surveillance footage helped investigators retrace Robinson’s route before the attack from a McDonald’s at the Twin City shopping plaza in Somerville to Warren Street in Cambridge, near the scene of the alleged attack, according to prosecutors.

Additional video footage captured Plaza on a bike “in the aftermath of the incident as he fled the scene,” the statement said.

Plaza was interviewed by investigators and denied any involvement in the attack, according to the filing, though he did say that he rode his bike on Cambridge Street on the night of the incident, according to the statement.

Investigators, however, learned that he told a witness he had “pushed her by accident,” the filing said. He also told authorities that the sneakers he wore on the night of the attack were stolen while he was asleep, and that he left the bicycle unsecured “so someone would take it because he had been on it on Cambridge Street that day,” the document said.

Asked about the bike’s whereabouts, Plaza allegedly told investigators, “it’s gone.”

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He said he had burned the sweatshirt and pants he wore that night “because he was worried about being associated with this incident,” the statement said.

Robinson’s family declined to comment after Tuesday’s arraignment.

Robinson had attended the youth academy at the Cambridge Police Department, which honored her family at the academy’s 2018 graduation ceremony. Her family organized a march in her honor last July, attended by more than 100 people.

“She had future plans to become an emergency medical technician,” her family said last year as part of the march. “She loved to dance and she loved makeup and getting her nails done.”

Plaza had been arrested in Cambridge several weeks before Robinson’s death, according to court records. On June 6, 2018, legal filings show, Plaza was arrested for allegedly trespassing on the Rindge and Latin campus and earlier stealing someone’s dog, a Staffordshire Bull Terrier valued at $1,000.

At the time, he was dating a student at the high school, who wasn’t named in a redacted copy of the police report.

Two days before Plaza’s arrest for allegedly trespassing, a female had gone to the Cambridge police station to report that Plaza physically assaulted her on June 2 after she rejected his sexual advances, according to a separate police report.

According to that report, Plaza punched her in the arm, leaving a bruise, and threatened to stab her with his pocket knife if she told anyone. He was charged with assault and battery in that matter. It wasn’t immediately clear Tuesday how the June 2018 cases were resolved.

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The next hearing in Plaza’s manslaughter case is slated for Aug. 13.


Travis Andersen can be reached at tandersen@globe.com. Follow him on Twitter @TAGlobe. John R. Ellement can be reached at ellement@globe.com. Follow him on Twitter @JREbosglobe.