NEW YORK (CBSNewYork) – A third suspect has been arrested in the stabbing death of Barnard College freshman Tessa Majors, police sources tell CBS2.

Luciano Lewis, 14, turned himself in to investigators this morning and was charged with murder and robbery as an adult, sources said.

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In a pink plaid shirt and camo jacket, his hands handcuffed behind his back, Lewis was led into court Wednesday to be arraigned right next to his reported accomplice and the teen who allegedly use the knife, Rashaun Weaver.

Tessa Majors (Credit: Conrad MacKethan)

Police arrested 14-year-old Weaver last Friday at the Taft Houses in Harlem. He will also be tried as an adult.

An unnamed 13-year-old was arrested last December.

Police said all three teens tried to rob Majors, but it was Weaver who actually stabbed her in Morningside Park.

“We are confident that we have the person in custody who stabbed her, and that person will face justice in a court of law,” NYPD Commissioner Dermot Shea said Saturday.

Majors was a freshman with big dreams. She played in a rock band and was considering a career in journalism.

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Watch: NYPD Commissioner, Manhattan DA Announce Weaver Arrest 

Court documents reveal a heartbreaking struggle, with Majors desperately fighting to survive – clawing at the boys, even biting Weaver, according to police sources.

“It paints a gruesome picture of what this young woman endured in her final moments. As alleged, some of the last words she was known to have said was, ‘help me, I’m being robbed,’” said Manhattan District Attorney Cy Vance.

DNA evidence helped incriminate Weaver, plus witness statements, including some from the suspect himself.

Web Extra: Read The Complaint Against Weaver (.pdf)

He was indicted by a grand jury, which heard from 20 witnesses and examined hundreds of pieces of forensic evidence from the crime scene, including the murder weapon and surveillance video.

“Sadly, it cannot bring back this young woman, this student, this victim,” Shea said.

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Both Weaver and the latest suspect were expected to be arraigned Wednesday afternoon.