Josef Neumann, one of the victims, died three weeks ago.

A judge declared the suspect who allegedly killed a man and slashed four others with a machete during a Hanukkah celebration was mentally unfit for trial and ordered him to undergo mental health treatment to assess his competency.

U.S. District Court Judge Cathy Seibel ordered that Grafton Thomas be treated at a suitable facility to determine if he “will attain the capacity to permit criminal proceedings to go forward against him,” according to the court order issued Monday. The treatment would not exceed four months and the Federal Bureau of Prisons will provide a report on any updates to the court within the first 30 days, the order said.

Thomas, 37, allegedly forced his way into the Monsey, New York, home of Rabbi Chaim Rottenberg while he hosted the celebration with other Hasidic Jews on Dec. 28 and attacked the group, police said. He was arrested a short time later.

Josef Neumann, 72, one of the victims, succumbed to his injuries and died March 29.

Federal and state prosecutors, who have indicted Thomas on several charges including hate crimes, murder and attempted murder, contend he targeted the house and the guests because they were Jewish. Thomas allegedly had handwritten journals containing anti-Semitic comments and had researched Adolf Hitler’s hatred of Jews online, according to prosecutors.

Thomas’ attorney Michael Sussman, has argued that Thomas suffers from “severe psychiatric issues” and has had psychiatric hospitalizations in the past.

“I have stated from the very outset that, based upon my investigation, this was not an act of domestic terrorism,” Sussman told ABC News in a statement following the ruling. “While others were making that claim and inflaming the public, I stated that Mr. Thomas had a long well-documented history of mental illness and that, tragically, this motivated his conduct in late December.”

“The medical reports received by the courts being to explicate this history … his actions on the night in question all bespeak to his very serious mental illness,” Sussman continued. “In this situation, long-term treatment and hospitalization appear to be appropriate.”