警方：波士顿爆炸案一嫌疑人已丧生另一名在逃

Police in Massachusetts are conducting a massive manhunt for one of the suspects in Monday's Boston Marathon bombings, after killing the other suspect in a shootout late Thursday.  US media are reporting the suspects are brothers of Chechen origin.

Authorities say the "white hat" suspect from the marathon bombings, known as Suspect Two, is on the loose and is "armed and dangerous."  Police are searching through the suburb of Watertown, about eight kilometers from Boston, and other parts of the Boston metropolitan area.

The Boston region is in lockdown.  Residents have been urged to stay in their homes with the doors locked, public transit service has been suspended and all schools and universities are closed.  Officials have shut down airspace over Boston.

Massachusetts Governor Deval Patrick said the situation is "serious," and he asked the public to also take it seriously as well.

Boston police have identified the suspect at large as 19-year-old Dzhokhar Tsarnaev of Cambridge, Massachusetts, a town outside of Boston.  The deceased suspect is believed to be 26-year-old brother Tamerlan Tsarnaev. 

U.S. media say the suspects' family is from a Russian region near Chechnya, which has been plagued by an Islamic insurgency stemming from separatist wars.  The brothers were believed to be living legally in the United States.