Large numbers of BPD officers descended on the Esplanade and the BU Bridge shortly after 4 p.m., when a 911 caller reported a man in camouflage running around near the bridge with a rifle. Cambridge Police sent some officers to their side of the bridge as well.
In fact, it turned out there was a whole troop of men running around the Esplanade with rifles - but they turned out to be BU ROTC cadets doing some training with fake rifles.
When officers caught up with them, they said they had notified BU's own police department and BPD, although that was news to the officers. Seems that's a common ROTC training area.