Prosecutors say Joseph Horner asked Victoria Castle to help move a piano before attacking her in his upstairs apartment.

NORTH MASSAPEQUA, N.Y. — A Long Island elementary school music teacher is being held without bail after authorities accused him of killing his 25-year-old sister-in-law inside a multifamily home where the two lived in separate apartments.

Joseph Horner, 27, pleaded not guilty to second-degree murder after his June 29 arrest in the death of Victoria Castle, according to police and reports from his arraignment. Prosecutors said Horner asked Castle to come to the apartment he shared with his wife by telling her that he needed help moving a piano. Once Castle was upstairs, authorities allege, Horner approached her from behind and placed her in a chokehold until she became unconscious. Prosecutors further alleged that he sexually assaulted her after she lost consciousness. Horner has not been convicted, and the allegations against him remain subject to litigation in court.

The Nassau County Police Department said officers were sent to a North Oak Street residence at 8:44 a.m. after receiving a 911 call requesting an ambulance for a woman who was not breathing. Officers found Castle unresponsive and began efforts to revive her. She was taken to a nearby hospital, where she was pronounced dead. Police arrested Horner at the scene and charged him with second-degree murder. The department’s initial public statement did not describe a motive or provide the detailed account later presented by prosecutors at the arraignment.

Prosecutors said Horner himself placed the emergency call and was waiting outside when police arrived. According to their account in court, he had changed his clothes before calling 911 and then remained on the front stoop. Authorities have not publicly released the complete recording or transcript of the emergency call, nor have they released any full written or recorded statement attributed to Horner. The prosecution’s description of what Horner allegedly said to investigators is expected to become important as the case proceeds and the defense considers whether to challenge the admissibility or meaning of any statement.

The events unfolded in a house divided into separate living spaces. Horner and his wife lived in an upstairs apartment, while Castle lived in another unit, according to prosecutors and local news reports. Horner’s wife, who is Castle’s sister, was away at a bachelorette party at the time, authorities said. Prosecutors alleged that Horner used the request involving the piano to bring Castle into the upstairs residence. The account places the alleged attack in an ordinary family setting and centers the case on what authorities say occurred during a brief period when other relatives were away.

Authorities also alleged that Horner told investigators he had been interested in Castle since 2017. That assertion has been reported as part of the prosecution’s description of the case, not as an independently established motive. Officials have not released evidence showing when any alleged plan was formed, whether Horner communicated those feelings to Castle or anyone else, or whether there had been earlier complaints involving the two. No public report reviewed for this article described a documented history of violence between them. Those unanswered questions may become relevant as prosecutors seek to prove intent beyond a reasonable doubt.

Castle was pursuing advanced study in geosciences at Stony Brook University. A university profile published in 2023 described her work in luminescence dating, a method used to estimate when mineral material was last exposed to light or heat. Her research included efforts to establish the age of deposits connected to the Udorka River in southern Poland and to study the chronology of ancient structures in Oaxaca, Mexico. The profile said she had presented research at a national Geological Society of America meeting and hoped to contribute to geochronology, geomorphology and the study of recent geological periods.

The university profile portrayed Castle as a young scientist building the skills needed for independent research. She discussed the care required to prepare samples and the value of using small pieces of material to understand events from the distant past. She also credited research fellowships and mentors with helping her present scientific work and connect with other women in the field. Local coverage following her death identified her as a graduate student working toward a doctorate. Stony Brook’s description of her earlier work provides a public record of the professional path that was cut short by her death.

Horner worked as an elementary school music teacher in the Oceanside School District. After his arrest, the district said he had been placed on administrative leave effective immediately while officials conducted a further review. The district said it had no additional information to release. That action is an employment measure rather than a criminal finding. It removes Horner from his school duties while the criminal proceeding is pending and while district officials assess any separate personnel issues raised by the arrest.

At Horner’s arraignment, defense attorney Gregory Grizopoulos emphasized his client’s standing in the school community, describing him as a tenured teacher who was well regarded by students and colleagues. The attorney said the accusations did not fit the person Horner’s relatives, friends and co-workers believed they knew. Those remarks did not address the prosecution’s evidence in detail. A defendant’s reputation and employment history do not determine criminal liability, just as an accusation alone does not establish guilt. The case will turn on evidence presented through the judicial process.

Second-degree murder is a class A-I felony under New York law. The statute includes intentional murder, in which prosecutors must prove that a defendant intended to cause another person’s death and caused that death. Local reporting said Horner could face a sentence of 25 years to life if convicted of the charged offense. The precise legal theory prosecutors will pursue, along with any additional charges they may seek, will depend on the formal charging documents and evidence presented as the case moves beyond the initial complaint.

An arraignment is the first court appearance at which a defendant is informed of the accusations, advised of legal rights and asked to enter a plea. Horner’s not-guilty plea preserves his right to challenge the allegations and require prosecutors to prove their case. Because the accusation is a felony, prosecutors may present evidence to a grand jury, which determines whether there is legally sufficient evidence to issue an indictment. A grand jury’s decision to indict would not be a finding of guilt. It would permit the prosecution to continue toward further hearings or trial.

Future proceedings could address the medical findings concerning Castle’s death, forensic evidence collected from the home, the circumstances surrounding Horner’s alleged statements and any digital or physical evidence that prosecutors believe shows planning or intent. None of those materials had been fully released in the public accounts reviewed for this article. Authorities also had not publicly identified additional witnesses to the alleged attack. The defense will have an opportunity to examine the prosecution’s evidence, seek relevant records and file motions challenging evidence or legal procedures.

The case has left one extended family confronting both Castle’s death and the accusation against the man married to her sister. Relatives from both sides attended the early court proceeding, according to local coverage, but declined to discuss the case publicly. Their presence reflected the unusual overlap at the center of the prosecution: The accused man, the victim and Horner’s wife were connected not only through family ties but also through their residence in the same North Massapequa house.

Horner remained in custody without bail following his not-guilty plea. Police described the investigation as continuing, and the publicly available reports did not establish whether prosecutors had obtained an indictment or added charges after the initial arraignment. Any later determination of guilt or innocence must be made in court on the basis of admissible evidence. Castle’s death, however, is not in dispute: She was found unresponsive in the family home, taken to a hospital and pronounced dead on June 29.

Author note: Last updated July 28, 2026.