An 18-year-old from Massachusetts has been taken into custody on murder charges after a resident reported seeing him with a bloody knife in her neighborhood.

Anthony DeMayo faces charges of murder and home invasion following his admission to the killing of 68-year-old Janet Swallow in her Danvers residence on Wednesday. The Boston Globe reports that DeMayo was apprehended on Thursday after a local woman observed him wandering her street, wielding a large knife and mimicking stabbing motions in nearby bushes. The eyewitness described the teenager as appearing “unhinged, and I think mentally unwell,” prompting her to call 911.

Authorities quickly located DeMayo, who allegedly informed them that he had murdered a woman in Danvers the previous evening.

Court records reviewed by The Boston Globe reveal DeMayo’s confession to cruising around Danvers in search of a house to burglarize. He ultimately targeted Swallow’s home, gaining entry through a kitchen window. As per the documents, DeMayo admitted to entering several rooms before discovering Swallow asleep in her bed, where he proceeded to stab her in the neck.

DeMayo allegedly recounted that when his knife became lodged in Swallow’s neck, he dragged her from the bed to the floor. After reportedly leaving her to succumb to her injuries, he returned to his residence in Lynn, Massachusetts.

Police tracked DeMayo’s cellphone, placing him in Danvers, where the device remained stationary between midnight and 1 a.m. on Thursday, according to reports.

The Boston Globe reported that after DeMayo was arrested, he indicated to investigators that “he planned on committing this act for a long time, and wanted to kill someone for a long time.”

The woman who called 911, Ashley O’Brien, spoke to local ABC affiliate WCVB about seeing DeMayo the afternoon after he allegedly murdered Swallow. O’Brien said, “He looked right in my eyes, and I just kind of looked away. And once he left, I just knew I had to call the cops because, I mean, he was definitely looking to hurt somebody.”

During a press conference on Thursday, Essex County District Attorney Paul Tucker called the alleged murder “random” and said that there was “no connection” between DeMayo and Swallow.

Swallow was an ICU nurse who left behind two adult sons. Local NBC affiliate WBTS reported that DeMayo was a high school senior at Bishop Fenwick High School. The school’s president, Tom Nunan Jr., said counselors were available on the campus for any students or staff who needed assistance.

DeMayo was scheduled to be arraigned in Salem District Court on Friday. He was charged with murder and home invasion.