US officials, carrying out their own investigation into the bombing of a Russian Metrojet in the Sinai Peninsula despite not having access to the crash site or any of the direct evidence, say that they believe bringing down the plane would’ve required a “military-grade” explosive, likely something along the lines of C4.
The bomb itself was unlikely to be particularly advanced, according to British FM Philip Hammond, who says that the working theory right now is a simple timer to set off the explosive payload. With a high-end explosive, likely only a couple of pounds would be needed.
ISIS in the Sinai Peninsula is known to have used C4 in previous bombing attacks, and the Egyptian military has at times recovered caches of the explosive in raids against militant compounds. C4 is described as readily available to buy across the Sinai Peninsula, and ISIS has shown some capacity of making their own.
US and British officials are expressing annoyance at not having been invited to directly participate in the investigation with Russia and Egypt, and warn that they may never be given enough access to independently determine exactly what happened.