Ch 7 just showed one suspect being loaded into a cruiser.. stark naked. Not sure how long ago.
My hunch is they stripped him to check for body bombs - possibly cavity search - not unreasonable IMHO.
He didn’t look to have been shot and was very much alive... so that means he’s at least a third “person of interest”.
If the LEOs stumble on to the cell’s HQ (Mosque?) there will likely be full scale urban warfare.
The marathon bombing was likely a “community project” of some sort, and the perps likely have local support systems.
They may never find the one still at large once he contacts his peeps.