kim barker reports for the independent, non-profit news organization propublica. she specializes in "dark money" from those so-called "social welfare" groups that keep the identity of their donors secret. andy kroll works in the washington bureau of "mother jones" magazine. he's a muckraking journalist whose exposÉs have opened eyes to campaign finance corruption as well as malfeasance in congress and in the banking business. welcome to both of you. >> thanks for having us. >> it's great to be here. >> both of you have talked about -- covered and talked about dark money. exactly, for the benefit of my viewers, what is dark money? >> dark money, these are organizations that can take unlimited amounts of money from billionaires or corporations or unions or anybody. and then turned around and spend money on political ads without saying who their donors are. they don't have to tell who the money came from. they do have to say what it's being spent on and where it's going, but they don't have to say who the donors are. >> yeah, where does all this money go? i mean, it

. >> barker, new york, for sam and his girlfriend, kim, october 3, 2008, began as an ordinary day. unphased by the darkening skies above. >> we get a lot of rain around here, so you really don't think much about the skies. >> we had some errands to do, so jumped into the truck and came to get gas. this is the gas station we got it here. >> this is the station we were at. >> pump three. >> pump number three it is. >> i left a little bit of me behind there at the pump. >> the score's surveillance camera captured what happens. that's sam dressed in hunting camouflage. >> paid for my gas, had a little conversation with the patrons inside. >> among them, amelia joy. it is just by luck that he's safe inside when an explosion rocks the gas station. >> while i was in the store, i went to the counter, to change my pump number. and that's when it all happened. >> kim is in the couple's pickup listening to the radio when suddenly a huge noise. >> i heard a sound, the truck shook. i hit the floor board. it felt like a bomb, to be honest with you. or that the gas pump blew up. >> sam shows us w