A Long Island music teacher is suspected of brutally raping and murdering his 25 year-old sister-in-law while his wife was on holiday.

Officials say that Joseph Horner, 27, had a grotesque fascination with doctoral student Victoria Castle, 25, and lusted after her for nearly a decade before attacking her on June 29, inside the North Massapequa, New York property where they lived in separate apartments.

Horner lived in the upstairs apartment of the multi-family house with his wife, while Castle resided in the ground-floor unit, according to the Nassau County District Attorney’s Office.

According to prosecutors, Horner, who had been married to castle’s sister for three years, waited until his wife left town on a bachelorette trip before allegedly luring Castle upstairs with a simple request: help move a piano.

Castle, reportedly went willingly. She believed she was helping with a mundane household task.

Investigators allege that once upstairs, Horner ambushed her from behind, placed her in a chokehold until she lost consciousness, and then sexually assaulted her.

Court documents claim the attack was not random, but the culmination of years of alleged fixation. Prosecutors say Horner had been attracted to Castle since around 2017 and had been waiting for an opportunity when they were alone.

Long Island music teacher Joseph Horner 27, has been accused of brutally strangling his sister in law Victoria Castle, 25, to death and then sadistically raping her unconscious body

Victoria Castle, 25, was studying for her PhD at Stony Brook University prior to her sudden death

The attack allegedly took place in their shared North Massapequa home June 29.

After the alleged assault, Horner is said to have changed his clothes and dialed 911 himself, requesting police and medical assistance. 

‘The male caller requested police and an ambulance to this location for a deceased female,’ Daniel Steller, deputy commanding officer of the NCPD Homicide Squad, said.

Emergency responders arrived at the property where CPR was administered, before the woman was taken to a nearby hospital, where she was pronounced dead.

The 27-year-old’s wife was at a bachelorette party at the time of the attack, police said.

‘He’s married, he has been married for 3 years, and his wife was not home at the time of this incident,’ Steller said.

Horner was taken into custody at the scene.

In court, prosecutors alleged he admitted during questioning that he had long harbored erotic feelings for his sister-in-law and acted deliberately while his wife was away. He has not entered a guilty plea and is charged with second-degree murder.

His defense team disputes the allegations, saying they are inconsistent with his beloved character and insisting he maintains his innocence.

Horner’s wife/Castle’s sister was away on a bachelorette trip at the time of the deadly assult

Horner had asked Castle to help him move a piano to his upstairs apartment and Castle had obliged willingly, with no idea of the events to follow

After the attack officials suspect Horner changed clothes before ringing emergency services in a heinous ploy for assistance, later admitting to detectives that he had committed the act

In a resurfaced instagram post the Long Island doctoral student who was allegedly raped and strangled to death by her obsessed brother-in-law gushed over him in a haunting Facebook post after he married her sister.

‘My sister, my person, my partner in chaos, is now married to one of the most wonderful people in the world,’ reads Victoria Castle’s message accompanying a photo of her accused killer Joseph Horner sharing a post-nuptials kiss with her sister at their wedding venue.

‘He’s an Oceanside teacher, he’s tenured, he’s very well loved by his students and his colleagues; these allegations are not very in line with what his community friends and family believe,” attorney Gregory Grizopoulos volunteered.

It was an emotional scene, as Castle’s family cried and hugged one another in the courtroom.

Horner’s family was also present, and neither wanted to comment on the allegations.

The case has sent shockwaves through both the education community and academia.

Horner worked as an elementary school music teacher in the Oceanside School District, where he has since been placed on administrative leave pending the outcome of the criminal proceedings.

Castle was remembered by Stony Brook University as a promising young scientist pursuing her doctorate in geosciences. Colleagues described her as dedicated, bright, and deeply committed to her research.

The tragedy has also drawn attention to a haunting social media post Castle wrote years earlier, shared on the day Horner married her sister.

In it, she gushed praise, describing him as ‘one of the most wonderful people in the world’ and wished the couple happiness — a message that has since taken on a devastating new meaning in light of the allegations.

As the investigation continues, prosecutors say forensic analysis and further interviews are ongoing to build a full timeline of events inside the home.

Horner remains held without bail. If convicted, he faces a sentence of 25 years to life in prison.

The Daily Mail has reached out to the NYPD and Allison Horner for comment.