His defense attorneys said he was mentally ill and unfit to stand trial.
Kadar was formally charged by the U.S. Justice Department last year.
His mother previously defended her son by claiming his alleged behavior was caused by serious health problems.
“After the police were here, and when I understood what he did, I was shocked and horrified,” she told NBC News.
She added that she had no idea what her son was up to, and that the first she heard about the bomb threats was on the news.
“I thought it was done by someone who is anti-Semitic,” she said.
An unsealed FBI search warrant last year laid out how Kadar used a black market site known as AlphaBay to sell his hoax services on the “dark web.”
AlphaBay was shut down last July. Attorney General Jeff Sessions at the time called it “one of the most important criminal investigations of the year.”