NBC Nightly News Full Episode - July 31

Tonight, the sudden flash flood emergency happening right now. The state of emergency across the Northeast. Roads suddenly washed out.This big rig nearly underwater. Other drivers trapped in their cars. Flood swamping factories as water cascades down over trains.Even a major space launch scrubbed on the launchpad in Florida. We're tracking it all. The face of a killer.Police say this man, an elementary school teacher, admitted to killing that couple hiking with their two young daughters in Devil's Den Park. ...