People across Boston and surrounding suburbs have been told to stay indoors amid a massive police manhunt for one of two brothers suspected of carrying out the Boston Marathon bombings.
Police are hunting Dzhokhar Tsarnaev, 19, after he escaped a shootout where another suspect, his brother, died.
"Stay indoors with the doors locked," the Massachusetts governor said.
Three people died and more than 170 were hurt when two bombs exploded near the finish line of Monday's marathon.
The FBI released several images of two men they were hunting in relation to the bombing, one wearing a white cap, the other a black cap.
Police said "suspect number one" had been killed early on Friday, and they were looking for "suspect number two", the "white-capped individual", later named as Dzhokhar Tsarnaev.
Reports said the black-capped suspect - widely named in the US media as Tamerlan Tsarnaev - was the fugitive's elder brother.
Both are said to be of Chechen origin, and are reported to have moved to the United States about 10 years ago.