The attack happened around 4:30 a.m. inside the building on West 129th Street in Manhattan.
Police say the suspect was caught on surveillance camera waiting for his victim in the third-floor hallway of her building.
When she arrived, the suspect stabbed her multiple times all over her body.
She was rushed to Mount Sinai Morningside in critical condition, where she was pronounced dead.
Her name has not been released. However, her neighbors and friends say she was a mother to four young children, and lived with them and her mother.
Neighbors said she mostly kept to herself but was often seen with her children and was always pleasant.
"It hurts just to see you know, happened to a young girl I know of," said neighbor Ella Thomas. "My daughter is her age that was raised in this building."
Neighbor Basilio Gonzalez said he saw the blood on the stairs, and learned that the murder victim was his neighbor who he had been friendly with for about 20 years.
"She's a good woman, and she had four kids. It's bad," Gonzalez said.
Police say a person of interest was taken into custody at the hospital where he was being treated for injuries apparently suffered during the stabbing.
He is believed to be the victim's ex-boyfriend. No charges have been immediately filed.
"This seems like something more passionate and possibly domestic violence, that hasn't been confirmed as that, but the person who did this, something is wrong with them in terms of mind and spirit," said Dr. Iesha Sekou with Street Corner Resources.
The surveillance video has not been released.
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