Police on Friday night arrested one suspect in the Boston marathon bombing, Dzhokhar A. Tsarnaev, in a boat stored in a driveway in Watertown, Mass., following a daylong manhunt. A second susptect, Tamerlan Tsarnaev, Dzhokhar’s brother, died in a shootout Thursday night after a police officer was killed at MIT and the suspects led police on a chase that ended in explosions and gunfire.