East Setauket's Kacy Corso pleads guilty in connection with ex-boyfriend's stabbing near Stony Brook Yacht Club

An East Setauket woman will likely be sentenced to 7 years in state prison after pleading guilty to manslaughter in connection with the fatal November stabbing of her former boyfriend outside the Stony Brook Yacht Club last year.

Kacy Corso, 34, received the offer of a reduced charge by agreeing to fully cooperate with prosecutors in the second-degree murder case against codefendant Victor Panebianco, who she said chased down Christopher Millwater, 52, of Selden, and stabbed him to death Nov. 10. Corso had been facing 25 years to life in prison on her own murder charge.

“She accepted responsibility,” defense attorney Christopher Gioe said outside the courtroom Wednesday. “She had a very limited role in what happened in this case.”

Gioe called it a “proper resolution” of his client’s case, saying she never left her vehicle during the stabbing and can better serve the prosecution by helping them secure a conviction against the man accused of committing the killing.

Corso admitted before State Supreme Court Justice Timothy Mazzei in Riverhead Wednesday to driving with Panebianco from North Carolina, where they had been living for a short time, to the yacht club, which she said Millwater was known to frequent.

Corso admitted driving her Honda Civic into Millwater’s vehicle so Panebianco could chase him down and stab him. She said they were intent on injuring the victim.

Mazzei, who denied a defense request to seal his courtroom for the plea hearing, expressed some frustration about the plea agreement.

The judge made Corso repeat that it was only her intent to “cause serious physical injury” to Millwater.

“What was the plan?” Mazzei then asked Corso.

“There was no plan,” she said softly.

As part of the plea, Corso also admitted in open court that Millwater was never physically abusive toward her at any point.

“In fact, you described him [to police] as a good person overall, is that correct?” Assistant District Attorney Sheetal Shetty asked.

“Yes,” Corso responded.

In addition to first-degree manslaughter, Corso also pleaded guilty to hindering the prosecution, a charge prosecutors will request to have vacated if she follows through in helping to secure a conviction against Panebianco.

Mazzei stressed to Corso that she should be grateful for the deal her attorney got for her. "I don't know how he did this," the judge said.

Mazzei also strongly advised Corso that she must cooperate fully with the probation officers who prepare her sentencing report and said if any new information comes out he may not honor the agreed upon 7-year sentence.

Prosecutors had previously said Corso was in a long-term romantic relationship with Millwater that ended badly. Before the stabbing both Corso and Panebianco, whom she was dating, accused Millwater of harassing her in posts on Facebook.

At her arraignment in December Shetty said police-worn body cameras captured Corso saying she was afraid of what she might do to Millwater.

Video surveillance showed the couple going to the yacht club, Corso used her car to block Millwater's vehicle in the parking lot while Panebianco ran toward him with a knife shortly after 3:30 a.m.

Prosecutors had said Millwater tried to drive away when Corso drove "full force" into his car, sending it spinning through the parking lot.

Millwater began running from Panebianco, who prosecutors said was chasing him with a knife, while Millwater was yelling for help. Panebianco allegedly cornered Millwater and straddled him.

Prosecutors said the couple fled the state the same day, with license plate readers tracking them across four states to North Carolina.

Corso admitted Wednesday to fleeing the state to avoid prosecution but Suffolk police ultimately recovered the vehicle, clothing and a knife.

Her sentencing was tentatively set for September.

Panebianco is due back in court July 30, court records show.

By Grant Parpan

grant.parpan@newsday.com@GrantParpan

Grant Parpan covers Suffolk County courts and federal courts for Newsday. A Long Island native, he joined Newsday in 2022.