so what the heck happened out there? that's what we want to hear today when the executives finally spill their guts. they'll get a grilling from senators at the energy committee. that gets under way any moment. it's the first of two hearings for them today. we're talking about the big guns at bp, transocean and halliburton. each had a hand in the operations on the deep water horizon. now all in the deep water over the oil spill. cnn congressional correspondent brianna keilar is live on capitol hill. what will we hear from these witnesses? do we know. >> reporter: we've gotten some of the testimony ahead of time, kyra. so we will hear from the expert panel, a professor who maybe can give us some expert opinion as sort of a third party and then we're going to be hearing from the former head of the minerals management service which, you know, is the organization in charge of regulating the government officials in charge of regulating this, but what's really interesting is the second panel because you've got bp which was leasing the rig.