NY Post is reporting that Boston PD have a suspect in custody (they're going with the 12 dead number too).
A federal law-enforcement source confirmed to The Post there are at least 12 dead and nearly 50 injured. Fox News reported that Massachusetts General Hospital was treating 10 people with amputated limbs and all operating rooms were on hold.
Authorities have a identified a suspect, who is currently being guarded in a Boston hospital with shrapnel wounds.
As always with early reporting on these things, something in the above is bound to be wrong. Hopefully having the ******* in custody is right.