Egyptian investigators announced yesterday that "traces of an explosive substance" had been found on the bodies of "some" victims of Egyptair flight MS804 which crashed into the Mediterranean sea last May. The claim, which hints at a terrorist attack, has been greeted with scepticism because other evidence points to a fire on board. 

This is not the first time Egyptians have talked of an explosion on the plane, an Airbus A320. A few days after the crash the Associated Press quoted an unnamed Egyptian official as saying an explosion was "the logical explanation", based on the small size of the first body parts recovered. That claim was denied shortly afterwards by the head of Egypt's forensics authority.

In September, French investigators (who are involved because the doomed flight was from Paris to Cairo and the aircraft was designed and built in France) were reported to have found traces of TNT explosive on parts of the aircraft wreckage. However, the French complained that the Egyptians had prevented further examination.

Yesterday's announcement gave no details of the Egyptian tests, so it is difficult to judge their credibility. Commonly-used substances containing glycerin – some cosmetics, for example – can give false positive results when tested for explosives.

A spokeswoman for the French Bureau d'Enquêtes et d'Analyses (BEA) told Reuters:

"In the absence of detailed information on the conditions and ways in which samples were taken leading to the detection of traces of explosives, the BEA considers that it is not possible at this stage to draw conclusions on the origin of the accident."

As with the Russian airliner crash over Sinai last year and the killing of Italian student Giulio Regeni earlier this year, the Egyptian authorities seem more interested in coming up with explanations than suit them politically than in establishing the truth.

Promoting a terrorism theory in connection with MS804 might, at first sight, appear not to be in the Sisi regime's interests. They have been reluctant to accept it as the explanation for the Russian airliner crash (even though the evidence points in that direction) and it could cause further damage to Egypt's battered tourism industry.

However, the announcement about explosive traces aboard MS804 comes just a few days after the bombing of a cathedral in Cairo which killed 25 people, so it's possible the authorities are trying to link these two events.

Perhaps more importantly for the regime, though, a terrorist explanation for the crash would shift the focus of the investigation away from Egypt and towards France, raising questions about whether a bomb was planted on the aircraft in Paris. A report in the New York Times notes:

"In the early months of the investigation, senior Egyptian officials openly favored the bomb theory because it shifted potential blame away from the EgyptAir crew and the company’s maintenance record, and on to the security procedures at Charles de Gaulle Airport, where the flight originated."

Aside from the claims about explosive traces, other evidence points to a fire in the aircraft. Flight data indicated smoke in the avionics bay beneath the cockpit and in an adjacent lavatory. Mention of "fire" was also heard on the cockpit voice recorder.

No group has claimed responsibility for bringing the aircraft down, though IS claimed responsibility for the earlier Sinai crash.