Boston has imposed a broad and unprecedented lockdown on the city and its surrounding suburbs, as law enforcement officers search for the second Boston Marathon bombing suspect. The fugitive, identified as 19-year-old Dzhokhar Tsarnaev, escaped after a shootout in the suburb of Watertown in which his older brother, Tamerlan Tsarnaev, was killed. 

State and city leaders have urged businesses to stay closed. Schools were shuttered, including Harvard University and the Massachusetts Institute of Technology. The locus of activity is Watertown, where police, some traveling in armored vehicles, are going door to door in search of the suspect.

Massachusetts Gov. Deval Patrick (D) has urged all residents in the Boston area to stay inside for their own safety (the suspect is considered well-armed and dangerous), as well as to avoid getting in the way of police. "There is a massive manhunt under way," Patrick said. "We are asking people to shelter in place."

Residents of metropolitan Boston awoke to find their city "under siege," says The Boston Globe. Courthouses were closed. So were city and town halls. Garbage pickups were canceled. Police pulled taxis off the streets, and authorities halted service on subways, trains, and buses.

Residents who did leave their homes were confronted with eerily deserted streets.

Furthermore, authorities say the lockdown is necessary because further violence may ensue. "We believe this to be a terrorist," a police spokesman said in a news conference early Friday. "We believe this to be a man who has come here to kill people."

Adding to the sense of urgency, says David Weigel at Slate, "is the fact that police sources have suggested to CNN and other outlets that Suspect 2 may have explosives strapped to his body," since doctors said his brother's wounds included both gunshots and injuries from an "explosive device."

Police also asked for reporters and residents in the area for help. They ordered media not to broadcast "tactical positions of homes being searched," and asked people to report any sightings of Dzhokhar Tsarnaev, tweeting pictures of him: