Grafton Thomas, 37, of Greenwood Lake, NY, the suspect in an antisemitic stabbing attack in Monsey, NY, is led into Ramapo Town Court, Dec. 29, 2019. Photo: Seth Harrison / The Journal News, Rockland / Westchester Journal News via Imagn Content Services, LLC via Reuters.

A judge in New York ruled on Monday that the man accused of murdering one person and wounding four more during a frenzied stabbing attack at a Hanukkah party in Monsey last December was mentally unfit to stand trial on federal hate crimes charges.

Federal Judge Cathy Siebel wrote in her decision that the accused killer — 37-year-old Grafton Thomas of Ramapo, New York — was “suffering from a mental disease or defect rendering him mentally incompetent to the extent he is unable to assist properly in his defense.”

She ordered Thomas to be committed to a psychiatric institution for the next four months to determine if “in the foreseeable future he will attain the capacity to permit criminal proceedings to go forward against him.”

The judge cited a psychological report that was not disputed by federal prosecutors. Additionally, the ruling applies only to Thomas’s trial for federal hate crimes — he is also facing trial in a New York state court on charges of attempted murder.

Around 100 people were attending the Dec. 28 Hanukkah celebration when Thomas burst in wielding a machete. One of Thomas’s five victims — 72-year-old Josef Neumann — died from his injuries three months later.

Thomas is reported to have suffered from mental disorders in the past, and had been hospitalized on several occasions, according to members of his family.

Prosecutors revealed that he had kept a notebook filled with antisemitic statements and had run internet searches such as, “why did Hitler hate the Jews?”