He died of his injuries Sunday, Kohen said.
Dozens of people were gathered at Rabbi Chaim Rottenberg’s Monsey home to celebrate the holiday.
Thomas pleaded not guilty to five counts of attempted murder and was charged with a federal hate crime in January.
Michael Sussman, an attorney for Thomas told CNN that his client was hospitalized several times in 2019 and may have suffered a hallucination during the night of the attack.
Neumann sustained multiple stab wounds to his neck, arms and head, one of which penetrated his brain.
Those who knew Neumann described him a compassionate man.
Yisroel Kraus, who was also a guest at the rabbi’s home the night of the attack, told CNN in January that he considered Neumann a mentor and “incredibly kind human being.”
“One of the most selfless people I know,” Kraus said. “Since I knew him, he was a very poor man. He never had a dime to his name and always goes around collecting money for other poor families. It was never about himself.”
CNN’s Lizzie Jury contributed to this report.