be -- where the aircraft could be. >> for more on what search crews and crash investigators are facing out there, cnn's tom foreman is joining us. hey, tom. >> what they are trying to do in these difficult conditions right now is connect the dots. they know where the plane took off of course. they know where the plane wound up. they know where debris has now been found in that red box down there and they are dealing with currents out here. things that make it difficult. how do they connect the dots here and get really evidence in need. they work in three different layers. there's the surface layer. we talk about this debris floating on top of the water. we're not talking about critical keys as to what brought this plane down because that's not the type of thing that will tend to float out here. if you move from the first layer of the search into the middle layer where they start tracing those pieces on the top through the currents as they know them to exist here and then they can reach the third layer at the bottom down here and that's