this is obviously very good news for investigators? >> last night they thought they made a lot of progress in the what and how. tonight they believe they have made a lot of progress in the who about distributing the photo to law enforcement. i was told first by a source earlier today and confirmed by the mayor, that the big breakthrough came first, the video breakthrough was video that came through the service camera at the lord & taylor store. the video analysis of that showed them what they believe to be someone making the drop, coming in with a suspicious package and putting down right around the time. from that, they have analyzed that video more. boston pd are getting so much video sent in. from that, they made further progress in identifying, they do believe they have at least the second explosion site. video of the placement of the device.