That group, which was at the time on the State Department’s official list of terrorist organizations, has been described by its critics, like Trita Parsi of the National Iranian American Council, as “a cultlike Iranian terrorist organization with a history of violence and no support among the Iranian people.”

While his sources offered no hard evidence, Mr. Bahari said, the young men who stormed the building were chanting slogans — like “Death to the Islamic Republic” and “Death to Khamenei,” Iran’s ruling cleric — that are associated with the anti-Islamist M.E.K. That led to arguments and even physical fights with older protesters outside the base, who urged the younger men to refrain from violence and call for reform, not revolution.

In retrospect, Mr. Bahari said this week, “I think that moment really played into the hands of the government.”

The large and completely peaceful protest that came before the violence that day, Mr. Bahari said, was far more threatening to the authorities.