Prosecutors said he used a police shield to break a window, allowing other rioters to enter the building.
Letter found at the scene allegedly promises: This is just the beginning
A man allegedly told acquaintances that he wanted to kill House Speaker Nancy Pelosi, and travelled to DC with a rifle and hundreds of rounds of ammunition.
Louis Shenker, who surrendered to police on Tuesday, according to NBC News, was a BBYO regional vice president five years ago while in high school.
A police bomb squad arrived at the scene and are working to neutralize the explosives.
A police K-9 search of the area did not turn up any bombs.
Jewish Americans founded Brandeis at a time when many universities were closed to Jewish students.
The spate of threats recalls successive waves of bomb threats made against JCCs and other Jewish institutions in 2017, many of which led to building evacuations.