(CNN) -- [Update 9 a.m. ET]
A 13-year-old boy has been arrested in New York in connection with the death of Barnard College freshman Tessa Rane Majors, according to a law enforcement source familiar with the investigation.
The suspect admitted to the robbery attempt and stabbing and alluded to two other suspects, the source said Friday, adding that the investigation is ongoing related to other suspects.
Police observed the suspect Thursday in the lobby of a building near the neighborhood where the stabbing occurred, the source said. He was wearing clothing matching the description of clothes associated with the Barnard student incident.
The suspect was picked up on suspicion of criminal trespass, and police discovered he had a knife, the source said.
An 18-year-old student at Barnard College was stabbed to death just blocks from the Manhattan school in an armed robbery on Wednesday, Barnard College President Sian Leah Beilock said.
The student, freshman Tessa Rane Majors, staggered her way up to the "surface side" of Morningside Drive after being stabbed, according to Beilock, where she was found by a school security officer who called 911. She was taken to a local hospital where she was pronounced dead.
Majors had been walking through Morningside Park at 116th Street and Morningside Drive on Wednesday evening when police believe she was confronted by between one and three individuals, NYPD Chief of Patrol Services Rodney Harrison said. A struggle ensued and one of the individuals stabbed Majors with a knife several times.
There have been no arrests, but "a couple" of people are being questioned by police, Harrison added, stressing the investigation is still in its early stages. Those being questioned are minors, he said.
A knife was recovered but it's unclear if it's connected to Majors' murder, he said.
"I'm very confident ... that we're going to bring this individual to justice," Harrison said.
A law enforcement official familiar with the investigation previously told CNN a witness who spoke to the NYPD said Majors was confronted by 4-5 men during an initial dispute in Morningside Park.
Her cell phone was found a short distance away from where she was found, but she did not have a purse or wallet on her, the source said.
Majors is believed to be a victim of one of two robbery patterns in the area, the source said.
Pattern of crimes
Police officials and New York Mayor Bill de Blasio faced questions about the pattern of crimes in and around the park in Thursday's news conference. In response, Harrison said the NYPD had identified issues and implemented different strategies to combat the problem. The NYPD is stepping up patrols in and around the park and at the nearby schools, including Barnard.
"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 at the news conference.
"It's unbelievable to me that that could happen here, next to one of our great college campuses," he added. "It's an unacceptable reality."
The city has offered Barnard College any help it needs and it's sending mental health professionals to help students deal with the news, according to de Blasio.
"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," said Beilock, the college's president, adding a reminder that Barnard's public safety department provides 24/7 escort service for students.
'A personality no one could ever copy'
Majors' family is en route to New York City, Beilock said.
"Tessa was just beginning her journey at Barnard and in life. We mourn this devastating murder of an extraordinary young woman and member of our community," Beilock said.
People who commented on Majors' Instagram page and spoke to CNN described her as a kind young woman and devoted musician.
"She was one of the sweetest people I know. She had a kind heart," Lydia Pickering told CNN. As kids, she and Majors lived two houses down from one another in Waynesboro, Virginia, Pickering said. Majors was like an older sister, she told CNN.
"I can't even begin to explain the impact she had on me," Pickering said. "She brought joy wherever she went. She had a personality no one could ever copy, she was really just special."
Lexi Phelan, who met Majors this year at Barnard, shared two classes with her.
"Anyone who was lucky enough to meet her would agree that she was a good, kind person," Phelan said. "Her personality put others at ease and she lit up any room she was in with her passion."
Barnard College is an all-women's school in Manhattan with more than 2,600 students. The school's campus stretches from west 116th Street to west 120th Street off Broadway in the Morningside Heights neighborhood of New York City.
"The close-knit community at Barnard College is in shock right now," de Blasio said in a tweet. "We've lost a young woman full of potential in a senseless act of violence. I want every student and every member of faculty to know your city will be with you in the days ahead."