Investigators reportedly believe that the gruesome murder of an Upper West Side woman may have been perpetrated by a neighbor who gained entry to her apartment and cut her throat.

Just before 5 a.m. on Sunday, police arrived at 70-year-old Susan Trott's apartment on West End Avenue, following up on a call from a coworker who worried about Trott's well-being after a few days of silence. There, authorities found a trail of blood leading from the living room to the bedroom, where Trott lay face-up on the floor, her throat slashed. Police saw no signs of forced entry, and the apartment itself hadn't been robbed or—bloody mess aside—disturbed. Further, according to the NY Times, no visitors to Trott's apartment had signed in, and security footage didn't surface any persons of interest.

Investigators now believe, as the NYPD Chief of Detectives Dermont Shea said at a news conference Monday, "that all the pieces of that puzzle are in that building." According to CBS New York, as of Monday afternoon, authorities were focusing their efforts on a woman who lives in the building, although the nature of that woman's relationship to Trott remains unclear. Still, Shea told reporters on Tuesday that police had "executed a search warrant at a separate apartment within that building and recovered some items of evidence relating to the homicide," according to the NY Daily News.

"We are well aware of where they are," he added. "We have not had extensive conversations with the person of interest—but we will at some point."

The Times suggests that Trott may have had strained relationships with some of her neighbors, clashing on issues like whether or not they should let their dogs chase squirrels. An avid animal lover, Trott reportedly made a habit of scattering bird feed outside her building. Not all the residents seemed to appreciate that effort.

"She would throw bird seeds literally everywhere," Ruth Chiamulera, who lives in an apartment two floors below Trott's, told the Times. "It attracted lots of pigeons, but it also attracted lots of rats. That caused another problem. People were not happy with her."

Still, Chiamulera noted, the idea that they had a killer in their midst seemed to shock most residents. "I think that's going to really freak people out," she added. "I pretty much assumed it was someone she allowed into the building."

Others who knew Trott—an advertising freelancer and copywriter—described her more fondly. "It's like my mother has died," Eric Boscia, Trott's partner at the marketing firm Code Modern, told the Times on Sunday. "She was the greatest, most generous, kindest person I've ever known." Another former colleague, Martha Wetterhall Thomas, described her as "gutsy," recalling the time Trott chased down and tackled a man who snatched her purse. "She wasn't big, but she was a tornado kind of person."

This story is still developing, and we will continue to update as we learn more.