Pete Williams reports that although the identities of the suspects are not confirmed, the FBI thinks they know who they are--both with overseas military training, who have been in the U.S. for a year or so. 

It's approaching 5 a.m. in Watertown.  These are all places near where I used to live.  But a lot of people there probably have no idea what has gone on overnight, and the warnings not to answer their doors is something they haven't heard.  They're also considering not reopening the transit system this morning, as long as the second guy is at large.