(WNY News Now) – A 26-year-old Buffalo man has pleaded not responsible by reason of mental disease or defect in the May 2025 fatal stabbing of his 17-year-old sister.

Nicholas X. Allen, 26, of Buffalo, entered the plea Wednesday in Erie County State Supreme Court before Justice Debra Givens. An Erie County Grand Jury had indicted Allen on four counts related to the fatal stabbing inside the family’s North Buffalo home and alleged actions following the homicide.

Under New York law, a defendant may enter a plea of not responsible by reason of mental disease or defect only with the consent of the prosecution and approval of the court.

The Erie County District Attorney’s Office said prosecutors reviewed the evidence, psychiatric evaluations and the opinion of a forensic mental health expert before agreeing to the plea. The office determined Allen met the legal standard for a lack of criminal responsibility at the time of the offense.

The court accepted the plea after determining there was a factual basis for the disposition.

Allen will be committed to the custody of the New York State Office of Mental Health for examination and further court proceedings. Those proceedings will determine the appropriate level of confinement, supervision and treatment. He will remain under the jurisdiction of the court pursuant to New York Criminal Procedure Law Section 330.20.

“This case represents an unimaginable tragedy for this family, and my thoughts remain with them as they continue to grieve. While no legal resolution can undo the pain caused by the loss of a loved one, prosecutors have the responsibility to follow the law and pursue justice based on the evidence. We determined that this plea was the most appropriate and just disposition,” said DA Mike Keane.

The district attorney commended the Buffalo Police Department for its investigative work and victim advocate Kimberly Rapp for her assistance.

The case is being prosecuted by Assistant District Attorney Justin H. Caldwell of the Homicide Bureau and Assistant District Attorney Rachel Schepart of the Felony Trials Bureau.