[19:00:09] ERIN BURNETT, CNN ANCHOR:
OUTFRONT next, the bomb. U.S. officials telling CNN, major new details tonight saying a bomb loaded with military-grade explosives rigged to a timer likely brought down Metrojet 9268.
Plus, how can a bomb get onboard? We'll show you what airport screeners actually see and how hard it is to spot a hidden bomb. That's a special OUTFRONT investigation tonight.
 And breaking news, a plane crashing into a brick building in Ohio. The details are just coming in on this crash. We've got that for you as we are following it. Let's go OUTFRONT.

 Good evening, I'm Erin Burnett. OUTFRONT tonight on a bomb on a timer. U.S. officials telling CNN tonight that is what likely brought down Metrojet Flight 9268, killing all 224 people onboard. The timer set for just enough time to blow the plane up soon after take-off. We are also learning tonight that officials believe the bomb was a military grade explosive, specifically a plastic explosive like C-4. Also new tonight, officials believe an insider with access to the airport planted the bomb. Egyptian officials say they interviewed everyone with access to the plane including caterers.

Our Chief National Security Correspondent Jim Sciutto is OUTFRONT to begin our coverage tonight. And Jim, what more are you learning about the type of bomb that they think was used to bring this flight down?

JIM SCIUTTO, CNN CHIEF NATIONAL SECURITY CORRESPONDENT:
Erin, I'll tell you, U.S. intelligence is basically building a more detailed working theory here. And without the forensic evidence they've normally have with an investigation like this, access to the wreckage, to the bodies, U.S. intelligence officials more convinced it was a bomb that took this plane down. That it was likely snuck onboard by someone with access to the plane at the airport rather than a passenger. And it's based on the flash caught by a U.S. satellite as well as photos of the wreckage and other crews that it was likely military-grade explosives such as a C-4 that would be needed to cause a blast like this one. Now, they also believe as you said that a timer may have been used to detonate after take-off. Now, this is far from a conclusion, a final assessment, but it is a puzzle that they are trying to piece together from afar. And this is where they stand now.

BURNETT:
And I know that you're also, you mentioned that they say was an inside job not a passenger. Do they have any sense as to who? Was this someone who worked in cargo, someone who worked in catering, someone who didn't generally ever appear on the tarmac? I mean, do they have any sense at this point?

SCIUTTO:
Well, they've been looking hard. Egyptian officials telling us, they interviewed all airport staff that had access to this plane before take-off and that they've examined security camera footage. But in that investigation, they have not found evidence yet of someone putting a bomb on this plane. Now, we have this news our Rene Marsh reporting that Egypt has accepted an offer from the NTSB to travel to Egypt to visit that crash scene to take part in the investigation. This could be really an enormous step forward because what U.S. intelligence has lacked so far is access to that forensic evidence at the scene. And that access, if it follows through, the NTSB, could allow a more defensive judgment from U.S. intelligence.

BURNETT:
Al right. Thank you very much. I appreciate it, Jim Sciutto. And yes, as Jim saying, the breaking news that we have now that the NTSB, Egypt accepting their offer to help. Obviously, that could be incredibly significant as to this point. Egypt has denied any involvement by American investigators. But who is responsible for this crash? We now know the name could be the new Osama. New details about the possible mastermind behind this attack, our breaking wait tonight.

And Ben Wedeman is OUTFRONT.

BEN WEDEMAN, CNN SENIOR INTERNATIONAL CORRESPONDENT: (voice- over):
He goes by the nom de guerre Abu Osama al-Masri, a shadowy figure some say is the mastermind behind the downing of Metrojet Flight 9268.
It was his voice that claimed in an audio message that Wilayat Sinai, the ISIS-affiliated group waging an insurgency in the northern Sinai Peninsula, brought the plane down killing all 224 on board. But was he the mastermind?

When Abu Osama al-Masri does appear, his face is always blurred. And his real identity or any other details are equally blurry, although his accent is distinctly from mainland Egypt, not Sinai.