A solitary figure slipped quietly into the Capitol on the Friday afternoon leading to a Fourth of July weekend. He cradled a small package containing three sticks of dynamite. The former professor of German at Harvard University, Erich Muenter, came to Washington to deliver an explosive message. Although the Senate had been out of session since the previous March and was not due to reconvene until December, Muenter headed for the Senate Chamber. Finding the chamber doors locked, he decided that the adjacent Senate Reception Room would serve his purposes. He worked quickly, placing his deadly package under the Senate's telephone switchboard, whose operator had left for the holiday weekend. After setting the timing mechanism for a few minutes before midnight to minimize casualties, he walked to Union Station and purchased a ticket for the midnight train to New York City.

At 20 minutes before midnight, as he watched from the station, a thunderous explosion rocked the Capitol. The blast nearly knocked Capitol police officer Frank Jones from his chair at the Senate wing's east front entrance. Ten minutes earlier, the lucky Jones had closed a window next to the switchboard. A 30-year police veteran, the officer harbored a common fear that one day the Capitol dome would fall into the rotunda. For a few frantic moments, he believed that day had come. Jones then entered the Reception Room and observed its devastation—a shattered mirror, broken window glass, smashed chandeliers, and pulverized plaster from the frescoed ceiling.

In a letter to the Washington Evening Star, published after the blast, Muenter attempted to explain his outrageous act. Writing under an assumed name, he hoped that the detonation would "make enough noise to be heard above the voices that clamor for war. This explosion is an exclamation point in my appeal for peace." The former German professor was particularly angry with American financiers who were aiding Great Britain against Germany in World War I, despite this country's official neutrality in that conflict.

Arriving in New York City early the next morning, Muenter headed for the Long Island estate of J. P. Morgan, Jr. Morgan's company served as Great Britain's principal U.S. purchasing agent for munitions and other war supplies. When Morgan came to the door, Muenter pulled a pistol, shot him, and fled. The financier's wounds proved superficial and the gunman was soon captured. In jail, several days later, Muenter took his own life.