But the boyfriend turned out to be cooperating with authorities, and following a dramatic law enforcement ruse in which the cop was shown a picture on Friday morning of her husband appearing to be dead in his car, she allegedly began discussing her alibi with the boyfriend in case she was questioned, according to court records.
The boyfriend was wearing a recording device, according to authorities, and the entire conversation was captured on audio and video.
That's when investigators from the Federal Bureau of Investigation (FBI) and the New York Police Department (NYPD) moved in and arrested her.
Officer Valerie Cincinelli, 34, of Oceanside in Nassau County on Long Island, was charged with conspiracy to commit murder and held without bail following a hearing late Friday afternoon.
Prosecutors argued in a detention memo filed in court on Friday that "the evidence in this case is overwhelming."
"The defendant was captured on audio and video recording planning the murders, and, once she was advised that the murder of John Doe was effected, she was captured on audio and video planning her alibi and destroying evidence of her involvement in the crime."
Cincinelli, who has been on the job since 2007, had been on modified assignment since 2017 because of prior domestic incidents involving the boyfriend and the estranged husband, law enforcement sources said.
In the memo, prosecutors noted that Cincinelli's first husband obtained a restraining order against her in 2014, that both she and her estranged husband have existing restraining orders against each other, and that she had a "volatile history" with the boyfriend -- who tipped off authorities to the alleged murder plot.
Cincinelli first approached the boyfriend about having her estranged husband -- and the boyfriend's teen daughter -- murdered in February, and continued discussions with him in person and on the phone, according to court records.
The boyfriend told her he knew someone who would commit the murders for $7,000, which he would convert into gold coins to pay off the hit man. Cincinelli allegedly withdrew the $7,000 in cash from a Long Island bank in February, court records show. He then used the money to purchase five ounces of gold coins, according to authorities. The murders were supposed to take place last weekend, officials said in court records.
The estranged husband was to be murdered near his office on Long Island, and Cincinelli and the boyfriend allegedly discussed how the killing "would not look suspicious because the murder would take place in 'the hood' or 'the ghetto,'" according to court records.
At one point, according to court records, Cincinelli seemed to become anxious about why the boyfriend's teen daughter had not yet been killed. After the boyfriend allegedly informed her that the hit man would not commit the murder near the child's school.
"OK, so she leaves school, you said he knows exactly where she lives, right?" Cincinelli is alleged to have asked him. "So what's the problem?"
At another point she allegedly told the boyfriend to tell the hit man to “run her the [expletive] over, how about that."
On Friday morning around 10 a.m., Suffolk County police arrived at Cincinelli's home to notify her that her estranged husband had been murdered -- but it was all part of an FBI-orchestrated ruse.
"Then, almost immediately after the Detective left the home, Cincinelli began to discuss...her alibi -- specifically what she would tell the police if she were to be questioned about the death," prosecutors wrote in a detention memo filed on Friday.
Then, at 10:48 a.m, according to court records, an FBI agent posing as the hit man texted a picture of the husband, appearing to be dead in his car, to the boyfriend. Along with the picture, the agent texted a demand for another $3,000 in order to carry out the murder of the boyfriend’s minor daughter, identified in court papers as “Jane Doe.”
"In response, Cincinelli instructed the [confidential informant] to delete the text messages and photographs, citing her fear that law enforcement could subpoena the phone," prosecutors wrote.
The identity of the boyfriend was not disclosed in court papers, and it remains unclear how he first came into contact with the NYPD.
The target of the alleged attack -- Isaiah Carvalho Jr., according to his attorney Matt Weiss -- only learned of the purported plot on Friday.
"He found out today, just like everybody else," Weiss told ABC News.
Weiss said that his client is grateful to law enforcement officials and that "all things considered, he sounds OK."
Carvalho Jr. sued her for divorce in Nassau County, according to court records cited by the New York Post, and a trial was set to begin next month.
Weiss issued a statement late on Friday saying his client is "still in shock."
"At the outset, Mr. Carvalho would like to thank law enforcement for all of their diligent efforts," Weiss said in the statement. "Mr. Carvalho is still in shock and is attempting to process the events, which have transpired over the past 24 hours. At this time, Mr. Carvalho and his family would appreciate the press honoring their privacy."
It was not immediately clear whether Cincinelli had retained a defense attorney. She was represented in court on Friday by a federal public defender, who could not immediately be reached. The New York Police Benevolent Association, which represents New York police officers, did not respond to a request for comment from ABC News.
Cincinelli's father told ABC News that his daughter was being set up by the boyfriend, whom he declined to identify.
In a telephone interview as he drove north from his home in Virginia to New York City to try and assist his incarcerated daughter, Louis Cincinelli said the boyfriend had once accused her of pulling a gun on him and threatening his life, only to allegedly recant that accusation in criminal court in New York
"I don't know what happened but I do know my daughter and I knew this was not true when I first heard it. She was going out with some wacko pathological liar who had her locked up once before, saying that she pulled a gun on him and threatened to kill him, but then he went to court and said in open court, he recanted it and said he had made it up. Now ... she throws this bum out again and two weeks later this happens."
"But she's the biggest idiot for being with him," he continued. "I don't know. I don't understand these kids. But I know my daughter. She wouldn't do this. She's a domestic violence officer, and she knows that that's not the way to handle something like this, to knock somebody off."
Cincinelli worked as a domestic violence officer in the 106th Precinct in Queens, according to the NYPD, but had been working on the modified duty since 2017 in a unit that monitors video surveillance cameras at city housing projects.
"I guarantee you," the distraught father continued, "the bottom line is going to be that it turns out she didn't do this."
The FBI and the NYPD’s Internal Affairs Bureau brought the case against Cincinelli.
ABC News' Nicholas Tucker contributed research to this story. This story has been updated to reflect that Carvalho is Cincinelli's estranged husband, not ex-husband.