Four pieces of evidence point to a bomb planted by terrorists, possibly Islamic State (ISIS) militants, as the likely cause of the tragic crash of the Airbus A-321 Russian passenger jetliner over Egypt on Saturday, killing all 224 people onboard, aviation experts said as reported by the Daily Express.
First, Egyptian and Russian authorities revealed that the Metrojet aircraft carrying Russian tourists broke up in mid-air and "fell vertically."
Second, they also disclosed that the pilot did not make any distress call before the plane vanished on the radar screen, which could rule out mechanical failure as the cause of the disaster.
Third, debris was scattered over a large area of the Sinai desert, which supports the theory of a major onboard explosion.
Fourth, photos of the wreckage show the skin of the plane peeling outwards, suggesting a massive force from inside shattering the body of the aircraft.
Within minutes of the crash, ISIS immediately claimed credit, saying it was "in response to Russian airstrikes that killed hundreds of Muslims on Syrian land."
In its Arabic-language statement that was translated into English, the ISIS said: "The fighters of the Islamic State were able to down a Russian plane over Sinai province that was carrying over 220 Russian crusaders.
"They were all killed, thanks be to God."
But the claim was dismissed by the Russian and Egyptian authorities who pointed out that the plane was flying too high, 31,000 feet above ground, to be hit by a missile.
What they did not initially consider was the possibility that the plane exploded in mid-air not because of a missile strike but by a bomb that someone managed to put or carry inside the plane, French experts said, according to the Express.
An Egyptian civil aviation official agreed that it was possible the plane was brought down by an explosive planted onboard.
Egyptian President Abdel Fattah al-Sisi said on Sunday night that it was too early to determine the cause of the disaster, adding that an "extensive and complicated technical study" was needed.
But Egypt's civil aviation minister Hossam Kamal tended to give weight to the bomb theory, saying that "up until the crash happened, we were never informed of any faults in the plane, nor did we receive any SOS calls."
Moments after the crash, the ISIS released a dramatic video showing a plane falling through the air before exploding in a ball of fire and smoke. It has not yet been verified though whether the video was authentic.
Investigators are also looking into claims that shortly before the ill-fated flight took off, the co-pilot had called his daughter over the phone and told her that the aircraft's condition "left much to be desired."
In an interview with state-controlled Russian news channel NTV, Natalya Trukhacheva, the wife of co-pilot Sergei Trukhacheva, said her husband made the remarks during a phone call to his daughter just hours before the plane took off.
Moscow has announced that it will conduct a criminal inquiry into the disaster. Reports said police raided the offices of Metrojet to search for clues.
But a spokeswoman for Metrojet said: "This plane met all the standards required for our flights. If it had had any technical faults that would have meant it couldn't perform this flight it would not have flown."
The Russian plane took off from the popular Egyptian holiday resort of Sharm El-Sheikh bound for the Russian city of St Petersburg with 217 passengers, including 17 children, and seven crewmembers including the pilots on board. There was no report of any survivor.
More than 150 bodies, including five children, were later pulled from the wreckage.
