Officials said he planned to use the bomb to kill himself and gain attention for a political belief called sortition, in which politicians are chosen at random for office instead of being elected.
It was not clear whether Rosenfeld had a lawyer.
Rosenfeld “concocted a twisted plan to draw attention to his political ideology by killing himself on the National Mall,” U.S. Attorney Geoffrey S. Berman said in a statement.
In August and September, Rosenfeld sent text messages and letters to someone in Pennsylvania telling of his plans to detonate a bomb on the Mall, authorities said.
On Tuesday, the FBI raided his home in Rockland County and found a workable bomb in his basement. It was taken to a “safe location” in the county, officials said. Federal agents also found empty black powder canisters and a fusing system that could trigger an explosive.
FBI Assistant Director in Charge William F. Sweeney said that “Rosenfeld’s alleged plot could have claimed the lives of innocent bystanders and caused untold destruction.” He said a concerned citizen had tipped off investigators.
Agents said they think Rosenfeld was acting alone in the alleged plot.