The Boston Globe has the latest details — Watertown is in lock-down at this point: Search for Marathon Bombing Suspect Locks Down Watertown, Surrounding Communities.

Bombing suspect Dzhokhar Tsarnaev

WATERTOWN — With nearly a million residents of the Boston area hunkering down behind locked doors, heavily armed police are making their way through a 20-block area of this community, searching for one of the suspects in the deadly Boston Marathon terror bombings.

Colonel Timothy Alben, head of the State Police, said in a news conference shortly after 12:30 p.m. that there had been “no apprehension at this point,” but said the situation was changing moment by moment.

Local, state, and federal law enforcement officers, including the Secret Service, are undertaking a door-to-door search of the area in Watertown. K-9 teams, explosives experts, and SWAT officers are involved, said State Police spokesman David Procopio. Alben said the search was about 60 percent complete.

Authorities cannot rule out the possibility that the suspect is wearing an explosive vest, Procopio said.

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The dead suspect is Tsarnaev’s brother, a source said. Dzhokhar Tsarnaev is a native of Kyrgyzstan, the Kyrgyz state news agency said. He was studying at the University of Massachusetts Dartmouth, university officials said.

Alben alerted the public that there would be a controlled explosion by bomb experts this afternoon on Norfolk Street in Cambridge, where the two brothers lived. The explosions would make it safer for investigators combing through the home, he said.