Within a week of the crash, serious considerations were given to the notion that the plane had been intentionally brought down. The UK government said that in the light of further British intelligence, the crash "may well have been caused by an explosive device".[62] British aviation experts travelled to Egypt to assess airport security; the UK government Cobra emergency committee, chaired by the Prime Minister, considered their findings. The BBC reported that the British government thinks the incident was probably caused by terrorism based on intercepted transmissions between militants based in Sinai. These transmissions suggest that a bomb was put in the hold prior to takeoff. Although the British have not ruled out a technical fault, the BBC reports that is "increasingly unlikely".[63] Paul Adams, BBC world affairs correspondent, said that Prime Minister David Cameron's spokesperson left little doubt that the British government believed the aircraft was brought down by a bomb. Adams said that suspending flights both to and from a foreign country and insisting on your own technical experts assessing security demonstrated a lack of confidence in that country's own security measures.[62] Security experts and investigators have said the aircraft is unlikely to have been struck from the outside and Sinai militants are not believed to have any missiles capable of striking an airliner at 30,000 ft (9,100 m).[64][65]
US President Barack Obama made a statement on 5 November that the US government was taking the incident "very seriously", knowing that there was a possibility that a bomb was on board the flight.[66] At the same time, flights began to be stopped from and to Sharm el-Sheikh in Egypt, causing around 20,000 British tourists to be stranded.[67]
European investigators had found that the pit voice recorder data is consistent with an explosion and the flight data recorder cuts off abruptly.[68] On 8 November Reuters quoted an unnamed Egyptian investigation team member, speaking anonymously because of the sensitivity of the investigation, who said he was "90% sure" the airliner was brought down by a bomb, based on an initial analysis of the last second of the pit voice recording. Lead investigator Ayman al-Muqaddam said that other causes, such as lithium batteries overheating, a fuel explosion, or metal fatigue in the structure, still needed to be definitively ruled out.[8]
On 17 November 2015, the Russian security service chief Alexander Bortnikov announced that their investigation had concluded that a "terror act" brought down Metrojet Flight 9268 after traces of explosives were found in the wreckage. Spectral analysis was used among other methods to examine the substance found.[69] According to Russian officials, an improvised explosive device with power equivalent to up to 1 kilogram of TNT brought down the flight.[70][71][72][73] Russia offered a US$50 million reward for further information.[74][72] Reuters reported that, according to security sources, two employees of Egypt's Sharm el-Sheikh airport had been detained for questioning over the crash on su ion of putting a bomb on board the flight. Egyptian authorities denied this.[75]