8:00 AM PT: NBC's Kerry Sanders has been repeatedly pushed back from his positions, which makes it sound as though police are expanding a perimeter, but it's really not clear exactly what's happening.
8:03 AM PT: Grain of salt time: CNN reporting the activity may be related to police surrounding an associate of Dzhokhar Tsarnaev, the Boston Marathon bombing suspect.
8:08 AM PT:
At UMass-Dartmouth RT @Will_Richmond: Men in tactical gear have ordered a person to his knees at gun point
http://t.co/...
— @dbernstein via web
8:11 AM PT:
8:12 AM PT:
The Boston Police has just warned Twitter its overzealous citizen journalism is compromising their efforts and their safety.
— @mm via web
8:13 AM PT: WBZ broadcasting image of police breaking into a red car in Cambridge, but say it's unclear if there's anything of interest in the car, or if police are just trying to clear the streets.
8:28 AM PT: Mass. state police spokesperson sys what whoever was detained by authorities was not the primary suspect, Dzhokhar Tsarnaev.