[Cooper:] More breaking news tonight, the Egyptian government says it will allow NTSB investigators to take part in the Metrojet 9268 investigation. This would make them the first American investigators to be directly involved. Also tonight U.S. officials believe they now know what kind of explosive was used to take down the Airbus, as well as how it got on board and how it was detonated. Our chief national security correspondent Jim Sciutto joins us with the latest. What are you hearing from U.S. officials?
[Jim Sciutto, Cnn Correspondent:] Anderson, what they're doing now is building a more detailed working theory. This is without the hard forensic evidence you normally have with an investigation like this, access to the wreckage, to the bodies, the voice recorder, but U.S. intelligence officials more convinced that a bomb with a timer may have taken this plane down, that it was more than likely snuck on board by someone with access to that plane rather than a passenger, and based on a flash caught by a U.S. satellite as well as photos of the wreckage and other clues, that a military grade explosive, something like a c4 would be needed to cause a blast like this. To be clear, this is far from a conclusion or a final assessment, but they are trying to piece together the pieces of this puzzle from afar here.
[Cooper:] Do we know what steps the Egyptian government, Egyptian security took immediately after the crash?
[Sciutto:] They say they took serious steps immediately after the crash, that they interviewed and investigated every person who had access to this aircraft before that flight, including all the staff from SS Air, that is the company that serviced and catered the plane, this according to a Sharm el Sheikh airport employee familiar with security operations there. Egyptian officials say they also took control of all the cameras, all the sensors and related information at that air force even before announcing the crash that had taken place, but they have not made any arrests from the interviews or from that video footage they've watched.
[Cooper:] And this news that the NTSB will be able to join the investigation, do you have, know more details about this?
[Sciutto:] This is potentially a big deal. Our Rene Marsh first reported this, that Egypt has accepted a long-standing offer from the NTSB to travel to Egypt, to visit that crash scene and take part in the investigation. This could be key, because it gives you what U.S. intelligence has been lacking so far, that is access to forensic evidence, access that could allow for a more definitive judgment. For instance, if you're talking about a bomb, if you could test the wreckage for explosives residue, that will give you the answer. Was it a bomb and what kind of bomb was used. That's the step needed to be taken now so that U.S. intelligence can give a definitive answer on what happened here.
[Cooper:] Jim, I appreciate the details, Jim Sciutto. Up next, we'll check in with a group of voters in South Carolina and find out what they want to hear from the candidates tonight in Milwaukee.