Nanny Asked Ex-Boyfriend to Return Key. He Arrived With a Knife.

Karen Bermudez-Rodriguez wanted to break up with her boyfriend. And she wanted him to give back her keys.

Ms. Bermudez-Rodriguez, a 26-year-old au pair who lived with a family in a New Jersey suburb, exchanged text messages with the boyfriend, Joseph Porter, on Saturday at about 1:30 a.m., according to court documents.

Less than five hours later, Mr. Porter used the keys Ms. Bermudez-Rodriguez had previously given him to enter the home of her employer, and stabbed him to death, according to the authorities.

He then bound Ms. Bermudez-Rodriguez’s hands. When she fled, he chased her down the street with a knife.

The new details about the double homicide emerged on Monday as residents in Maplewood, N.J., a suburb 20 miles west of New York City, grappled with comprehending the loss that had struck the tight-knit community. A memorial of bouquets and notes cropped up near the township’s train station. “I love you, Karen. Thank you for being part of our lives,” one note read.

Mr. Porter, 27, of Elizabeth, N.J., was arrested on Sunday and charged with the murders of Ms. Bermudez-Rodriguez and her employer, David Kimowitz, 40, who managed comedians and owned the Stand Restaurant and Comedy Club, a comedy venue near Gramercy Park in Manhattan. Mr. Kimowitz’s wife and two young daughters were out of town at the time of the attacks, the authorities said.

Mr. Porter was detained on Sunday at Newark Liberty International Airport while, according to the police, he was attempting to flee the country for Cancún, Mexico. He was taken to the prosecutor’s office in Essex County, where the authorities noted he had visible marks and scratches around his neck, according to court records released on Monday.

According to the records, Mr. Porter told officers that he went to a home on Walton Road in Maplewood early on Saturday and stabbed Mr. Kimowitz in a second-floor bedroom. After Ms. Bermudez-Rodriguez fled — her hands bound with tape — Mr. Porter caught up with her on the street, 300 feet outside her employer’s residence, on Woodland Road, and stabbed her with a knife.

The police responded to the area at about 6 a.m., after a 911 caller reported hearing people fighting and had observed a woman being attacked. Ms. Bermudez-Rodriguez was found lying on the ground. She was transported to Newark Beth Israel Medical Center, where she died. The authorities found Mr. Kimowitz inside his home, where he was later pronounced dead. A knife was recovered near his body, according to the affidavit.

The authorities said they had recovered video at the scene that showed a man chasing Ms. Bermudez-Rodriguez down the street. Text messages the police reviewed from Ms. Bermudez-Rodriguez’s phone showed that Mr. Porter had been upset about the breakup. At least one of Ms. Bermudez-Rodriguez’s friends said she had ended the relationship with Mr. Porter last year.

Friends and acquaintances remembered Ms. Bermudez-Rodriguez, a native of Colombia, as a quiet but charismatic young woman. A photo left at her memorial showed her posing near the Brooklyn Bridge wearing an off-the-shoulder blouse and black hat. A friend, Valeria Rodriguez, had taken the photo a year ago.

“We went there to bid farewell to a friend, another nanny, who was returning to her country,” Ms. Rodriguez, 27, said. “She put that hat on and posed, because she loved taking photos. And she smiled. That’s how I am going to remember her, full of life.”

She said her friend had moved to the United States from Bogotá, Colombia, about a year and a half ago, leaving behind her mother and other relatives.