• Tessa Majors, an 18-year-old freshman at Barnard College, was killed in Morningside Park on Wednesday evening. 
• Police believe she was killed in a robbery gone wrong. 
• A 13-year-old who was arrested on an unrelated trespassing charge, admitted to murdering Majors after police discovered he was carrying a knife, police sources told CBS News.
• He is facing murder, robbery, and weapons charges according to sources who spoke to CBS.
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An 18-year-old freshman at Barnard College was killed in a stabbing at a Manhattan park, and an unnamed 13-year-old has been arrested in her death, according to police.

Tessa Majors, who grew up in Charlottesville, Virginia, was walking through Morningside Park on Wednesday evening when police believe she was stabbed in a robbery gone wrong, according to CNN.

NYPD Chief of Patrol Services Rodney Harrison told CNN that Majors had been confronted by one to three individuals who attempted to rob her, and she was stabbed with a knife several times after a struggle.

Majors made it to a nearby security booth to ask for help, but collapsed and later died from her injuries at Mount Sinai St. Luke's Hospital.

A 13-year-old who was arrested on an unrelated trespassing charge, admitted to murdering Majors after police discovered he was carrying a knife, police sources told CBS News. He was also wearing clothes matching the description of one of the people spotted at the scene.  

The teen told police that he and two friends tried to rob Majors of her phone and stabbed her. The 13-year-old is facing murder, robbery, and weapons charges, CBS reported.

New York Mayor Bill de Blasio said the stabbing was an "unacceptable reality" during a news conference on Thursday.

"The idea that a college freshman at Barnard was murdered in cold blood is absolutely not only painful to me as a parent, it's terrifying to think that that could happen anywhere," de Blasio said. "It's unbelievable to me that that could happen here, next to one of our great college campuses."

De Blasio said the city is sending mental health professionals to Barnard to help students deal with Majors' death.

Barnard President Sian Leah Beilock also cited mental health resources for students in a letter about Majors.

"This is an unthinkable tragedy that has shaken us to our core. Please know that we are all grieving together and I am thinking of you as we process this awful news as a community," Beilock said. "In these difficult circumstances, it is important for us to take care of each other."

On Thursday night, the Barnard campus held a vigil for Majors at the school's Diana Center. 

Barnard faculty members have given students a no-questions-asked extension offer for final exams, which are scheduled to take place Friday through December 19. If they wish, students can take the exams next semester, according to a campus letter seen by Insider.

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