Kacy Corso is expected to receive seven years in prison after pleading guilty, while Victor Panebianco now also awaits sentencing.

RIVERHEAD, N.Y. — Kacy Corso, the former girlfriend of a Long Island man killed outside the Stony Brook Yacht Club, has pleaded guilty to first-degree manslaughter and hindering prosecution, resolving the murder case against her as her co-defendant now also awaits sentencing after entering his own guilty plea.

Corso, 34, admitted her role in the Nov. 10, 2025, death of Christopher Millwater, 52, during a July 22 court appearance before state Supreme Court Justice Timothy P. Mazzei. She had originally faced a second-degree murder charge. Under the disposition reported in the case, Corso is expected to be sentenced Sept. 2 to seven years in prison. Her plea also requires her to cooperate with prosecutors. The case has changed further since her plea: Victor Panebianco, who prosecutors said carried out the fatal stabbing after arriving at the yacht club with Corso, pleaded guilty Aug. 11 to first-degree manslaughter.

The two admissions bring the prosecution into a new phase less than a year after Millwater was found gravely injured along Shore Road in Stony Brook. Suffolk County police said officers found him at about 3:40 a.m. outside 21 Shore Road, near the yacht club and marina. He was taken to Stony Brook University Hospital, where he was pronounced dead. Police initially announced only that Millwater, a Selden resident, had been the victim of violence. Investigators later arrested Corso and Panebianco, and a Suffolk County grand jury indicted both on second-degree murder charges in December.

Prosecutors said surveillance video and other evidence showed that the encounter began shortly after Corso drove into the yacht club parking lot with Panebianco as her passenger. Millwater arrived in his own vehicle and parked nearby. Authorities said Corso then positioned her vehicle in front of Millwater’s car. Panebianco got out and approached, while Millwater maneuvered around Corso’s vehicle and tried to leave. Prosecutors said Corso then drove into Millwater’s vehicle. Millwater got out and ran from the area, turning what had begun as a confrontation between vehicles into a pursuit on foot.

According to the prosecution’s account, Panebianco chased Millwater while swinging an object. Surveillance footage later described by the Suffolk County District Attorney’s Office showed Panebianco catching up with him. Authorities said Millwater was stabbed in the chest, suffering wounds that reached his heart and lungs. During the attack, prosecutors said, Millwater could be heard asking, “You’re stabbing me?” Authorities also said he called for help and for police. The reporting of those words became one of the most striking details to emerge from the evidence, but the broader case rested on video, phone records and the defendants’ movements before and after the encounter.

Corso’s own account at her plea hearing narrowed the state’s description of her role without removing her criminal responsibility. Asked about what she intended, she reportedly acknowledged an intent to cause serious physical injury to Millwater but said there had been no plan to kill him. When Mazzei asked what the plan was, Corso answered, “There was no plan.” Her defense attorney, Christopher Gioe, later said outside court that Corso had accepted responsibility and characterized her role as limited. The guilty plea to manslaughter nevertheless represented an admission to a serious felony tied directly to Millwater’s death.

Prosecutors had described Corso differently when the murder indictment was announced. Their account said she drove the vehicle that helped prevent Millwater from leaving and struck his car after he tried to escape. After Panebianco allegedly caught Millwater, prosecutors said Corso could be heard yelling during the attack. They said that after Millwater was motionless, Panebianco returned to Corso’s vehicle and she drove away. The hindering-prosecution count to which Corso also pleaded guilty reflected conduct connected with the aftermath of the killing, although publicly available accounts of the July plea have not provided a full transcript explaining every factual admission underlying that charge.

The relationship among the three people drew attention after investigators and reporters examined social media activity from shortly before the killing. Millwater was Corso’s former boyfriend, while Panebianco was described as her boyfriend at the time. A Facebook account in Corso’s name included earlier material suggesting that she and Millwater knew each other, and Fox News reported that Millwater had “liked” one of Corso’s posts in the days before his death. Prosecutors have not publicly established in the material reviewed that the social media interaction was the motive for the fatal encounter, and the Facebook activity should not be treated as proof of why the confrontation occurred.

Millwater had longstanding ties to the area where he died. His funeral home obituary listed him as a Selden resident and gave his life dates as Dec. 8, 1972, to Nov. 10, 2025. His sister told News 12 after his death that Stony Brook was his favorite place to fish. Fox News also reported that a social media post from Millwater said he had received an “all clear” in October after a battle with cancer. Those details emerged as his family and friends sought answers about why a routine waterfront setting became the scene of a homicide.

The investigation moved through more than one state. Corso was arrested in Suffolk County after police publicly identified her in November. Panebianco was taken into custody in North Carolina and later returned to New York. When prosecutors announced the December indictment, they said both defendants were residents of King, North Carolina. The district attorney’s office said investigators relied on surveillance footage, witness accounts and phone evidence in reconstructing the events. The state originally accused both defendants of acting together in a deliberate and coordinated assault, though their eventual pleas and expected sentences reflect different legal dispositions.

Panebianco’s Aug. 11 plea is now the latest major development in the prosecution. He pleaded guilty to one count of first-degree manslaughter before Mazzei, according to subsequent reporting based on the Suffolk County district attorney’s announcement. He is due to return for sentencing Sept. 22. The reported expected sentence is 25 years to life in prison. District Attorney Raymond A. Tierney said after the plea that an admission of guilt could not undo the loss suffered by Millwater’s family and friends but would spare them from going through a trial.

The substantially different expected punishments for the two defendants reflect the roles and agreements resolved through their pleas. Corso’s expected seven-year sentence followed her agreement to cooperate with the prosecution, while Panebianco faces the much longer term. Earlier reports had said he could face up to 25 years in prison if convicted of murder. His later manslaughter plea eliminated the need for that murder trial. The public reporting reviewed does not establish that either expected sentence has yet been formally imposed, and a judge retains the authority associated with sentencing proceedings under the plea arrangements placed before the court.

The two September hearings are now the next confirmed milestones. Corso is scheduled to be sentenced Sept. 2, followed by Panebianco on Sept. 22. Their guilty pleas mean the case has moved well beyond the posture described when Corso first changed her plea in July: both people originally indicted for Millwater’s killing have now admitted to manslaughter, leaving sentencing rather than a murder trial as the principal court business still ahead.

Author note: Last updated August 28, 2026.