A Nassau County music teacher accused of killing his sister-in-law was indicted on new charges Wednesday.

Joseph Horner, 27, of North Massapequa now faces two additional counts of murder and two counts of rape, according to the Nassau County District Attorney.

As News 12 has reported, the Oceanside educator allegedly strangled his wife's 25-year-old sister, Victoria Castle, to death last month.

Horner has pleaded not guilty to the charges and was remanded.

According to the indictment, police responded to a 911 call around 9 a.m. on June 29, and found Horner on the front stoop of the home. Inside, they discovered Castle on the ground-floor lying naked and unresponsive in her bed.

She was taken to the hospital and pronounced dead.

Officials tell News 12 the home on N. Oak Street was multi-family and split into two apartments, where the married couple and Castle all lived since 2024.

Prosecutors said about an hour prior to police arriving, Horner asked Castle to help him move a keyboard piano into his apartment while his wife wasn’t home. After moving the piano upstairs, prosecutors say he went back to the ground-floor to get the bench.

Once downstairs, Horner allegedly attacked Castle from behind and put her into a chokehold until she went limp.

He is then accused of taking off her clothes, putting her onto her own bed, and raping her.

An autopsy determined that her cause of death was strangulation.

Horner has allegedly admitted to lusting over his wife's sister for years and that day he saw an opportunity to follow through on his "sexual desire.”

“This vicious attack was the act of a deranged individual suffering from an unrequited love and sick lust dating back more than a decade," said Anne Donnelly, the Nassau County District Attorney, "Joseph Horner saw his chance when his wife was out of town, and he allegedly took it. Now, a bright young woman with a promising future is dead."

He is expected back in court on Aug. 19 and if convicted face up to life in prison without the possibility of parole.