A trail of blood led from one apartment to another. That was the first clue that led the police to suspect a 24-year-old woman in the fatal stabbing of her neighbor in an Upper West Side co-op.
Detectives made inquiries. The young woman, who lived with her mother, had been hospitalized for mental illness. A search of her apartment turned up other evidence, the police said, including blood on a shoe.
On Wednesday, more than a week later, the police arrested the woman, Anya Johnston, on charges she slashed the throat of Susan Trott, a 70-year-old advertising copywriter who lived one floor below her, the police said.
Ms. Johnston was charged with murder and burglary. The police said she was emotionally disturbed. The week of the murder, Ms. Johnston had been reported missing by her mother, but eventually had returned home, the police said. She told her family that she was mentally unstable and was taken to Mount Sinai St. Luke’s hospital on the day of the murder, the police said. She had undergone a psychiatric evaluation before she was taken into custody on Wednesday.
Her arrest marked a turning point in the investigation into a gruesome murder that rattled residents of the building and others in the Manhattan neighborhood.
Ms. Trott lived alone in a 14th-floor apartment of a prewar building on West End Avenue between 94th and 95th Streets. The police found her body faceup and fully clothed in her bedroom on Oct. 21. There was no weapon found at the scene, and there were no signs of forced entry. The medical examiner’s office said Ms. Trott died of a stab wound to the neck.
There were bloody footprints in the apartment, and in the hallway detectives discovered the blood trail leading from the victim’s apartment to Ms. Johnston’s apartment upstairs, where a search turned up other evidence related to the homicide, the police said.
Investigators eventually spoke with Ms. Johnston at a hospital before her arrest. Her motive remains murky, the police said.
From the moment Ms. Trott was found, the police said they had focused their investigation on a resident of the 93-unit building, which has surveillance cameras and a 24-hour doorman. But they did not publicly identify the person they wanted to question and revealed little else about the case until Wednesday.
Eric Boscia, a longtime friend and business partner of Ms. Trott, said that Ms. Johnston lived with her mother and knew Ms. Trott. Ms. Trott’s body was discovered after Mr. Boscia contacted the police from London, where he lives, and asked that they check up on her. He had not heard from her for several days.
“She was very spiritual and believed no one ever leaves this planet,” Mr. Boscia said.
A graduate of the Pratt Institute, Ms. Trott was an eccentric character known for her creativity and love of animals. Still, she angered some of her neighbors, who complained that her habit of feeding birds and squirrels attracted rats. Before her death, Ms. Trott confided in friends that she had received threats and that other residents in the building had harassed her.