TODAY   |  April 19, 2013

Authorities ‘think they know’ where bombing suspect is

NBC’s Pete Williams reports on the ongoing search for Dzhokhar Tsarnaev, a suspect in the Boston Marathon bombings who is still at large and believed to be extremely dangerous.

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This content comes from Closed Captioning that was broadcast along with this program.

>> what can you tell us? we want to connect the dots here a bit. we leave that kerry sanders is very close to this location where you have reported that authorities do feel they have this suspect at least surrounded in some sense.

>> they think they do. that's certainly the case. they can't be sure. they don't know what's in there. that's why you see all of this incredible preparation they're going through. they don't know if they're going to encounter gunfire or explosives or what and don't know if they're going to find him either. the him being dzhokar tsarnaev. the person identified by the fbi in the videos as the person with the white hat who they believe planted the second bomb at the boston marathon . they think they know where he is but they're not sure. i'm told that that is the reason for the extraordinary security in the area. while they think he's there, they can't be sure. and so to be extra cautious they told everyone in that entire region to stay inside. now, we had heard from a couple of law enforcement officials that there was also the possibility of a third person. a relative perhaps of these two that might be at large and could also be a threat. that concern seems to be fading now. so they're concentrating on just dzhokar tsarnaev who is someone who has demonstrated that he can kill and someone they believe was involved in planning two and planted two bombs, shooting of two police officers , one fatally, involved in an incident which his own brother was killed and then police say drove over his brother in the car to try to get away and eventually jumped out of the car and started this astonishing series of events this morning with entire communities, everyone told to stay inside. businesses told not to open. the mass transit system shut down. no fly zone over the city so that police helicopters can work unimpeded. it's just a remarkable situation and we're told no based on the concern about one man. now, you know, they demonstrated their knowledge of and capability and facility with explosives by setting the two bombs on monday, by throwing out additional explosives when the police chased them in the early morning hours of today. they say that the brother who was killed at the scene in watertown when he got out of the suv that they carjacked had explosives strapped to his body. perhaps they are also concerned the man they are still looking for, the younger man, the 19 year old, dzhokar, perhaps they are concerned that he has explosives as well.