A Customs and Border Protection (CBP) agent shot and killed his girlfriend, a nurse, in their New York City apartment before taking his own life in what police are investigating as a murder-suicide. The incident unfolded Tuesday night in the Bronx after the woman’s father, who was on the phone with his daughter, heard the shooting and alerted authorities.

Rudy Cantarini told The New York Daily News that he was on the phone with his daughter, Andrea Cantarini, 37, for 14 minutes as her boyfriend, Juan Cornelio Diaz, 38, held a gun to her head. He said his daughter had wanted to break up with Diaz, who he described as a "coward" who "couldn't handle it."

"I was just begging him to let her go. He just wouldn't do it," Rudy Cantarini recounted. He said Diaz told him, "It's over for her," before he heard gunshots and the phone drop. Diaz is a CBP agent based at John F. Kennedy International Airport.

Police responded to the apartment around 9 p.m. and found both Andrea Cantarini and Juan Cornelio Diaz dead from apparent gunshot wounds to the head. Officers are treating the incident as a murder-suicide stemming from a domestic dispute.

Neighbors reported hearing a loud argument earlier in the week. One neighbor, who identified herself only as Kaela, told The New York Daily News that she and her roommate had discussed calling the police before the argument stopped.

Andrea Cantarini had taken their six-year-old daughter to her parents' home earlier on Tuesday because Diaz was acting "irrational," her father told the New York Post. She returned to the apartment to retrieve belongings when Diaz, who was waiting in ambush, attacked her.

Neighbors described the couple as seemingly happy and loving, with one former neighbor, Karla Evangelista, telling The New York Daily News that Diaz would often play with their daughter in the parking lot and engage in long conversations. "He was a good-looking guy, always wearing nice clothes, always biking or running," Evangelista said.

Police stated that they had no prior domestic incident calls involving the couple. The firearm believed to have been used in the shooting has been recovered, and CBP has stated it is cooperating with the investigation. The couple’s six-year-old daughter was not present during the incident, and authorities are concerned for her well-being.

This story includes reporting from The New York Daily News, AMNY, and The New York Post.