Infrared satellite images released by US officials to media reportedly show a heat flash near the location of the crash when it happened.
The airline has also bolstered the terrorism theory, saying the disaster could only have been caused by what it calls “external factors” rather than technical faults or pilot error.
For the relatives of the 224 victims, the first task is to identify the dead. On a bleak St Petersburg day, many carried flowers as they arrived at the morgue. The task of finding out why this tragedy happened is expected to take much longer.
The airline insists there was nothing wrong with the plane or crew, fuelling speculation of foul play. Alexander Smirnov is the deputy general director of the airline Kogalymavia, owner of metrojet.
“There are no such faults, like engine failure, system failure, there is no such combination of systems failure, that could lead to a plane breaking up in the air. The only explanation of a mid-air break-up can be a specific impact. Some mechanical or physical impact.”
He couldn’t say what, or who, caused such a devastating impact.
The company argues the plane was in excellent condition, despite claims to the contrary by the co-pilot’s wife. It says radar data shows the plane suffered a catastrophic loss of speed and altitude, and that no emergency calls were made.
French aviation expert, Gerard Feldzer, says that sheds doubt on the possibility of mechanical failure.
“One thing is sure: If such a violent and sudden accident occurred, it might have been due to an engine explosion that could have set fire to the wing and led to the loss of control of the plane, which would have spun into a nosedive. Or, it also could have lost a part of its rudder. We can imagine this scenario but we can also imagine that the pilot in this situation would have sent a mayday distress signal since he was in contact with the control tower.”
The black boxes are being examined by a multi-national investigation team, but the results may not be able to solve this mystery, says Tony Cable, a former air accident investigator.
“If there’s a sudden structural failure, the recorders won’t necessarily show very much. So the flight data recorder could just well show everything normal – airspeed, altitude etc – everything normal, engine power and then the data just suddenly stopping.”
A source close to the investigation says early results suggest the plane was not struck from the outside. Theories of a bomb on board have been bolstered further, with infrared satellite images reportedly detecting a heat flash, when and where the crash happened. Aviation expert Gerard Feldzer agrees the possibility of a bomb can’t be ruled out.
“We can consider a terrorist attack with a bomb onboard. Because a missile is excluded – these people (Islamic State group) have neither the equipment nor the skills for that. But a bomb, which would have been introduced to the plane from checked bagage, is absolutely a possibility.”
The United States’ director of national intelligence, James Capper, said it’s too early to speculate on what may have caused the crash, and whether an IS affiliate group is to blame.
“Well, we don’t have any direct evidence of any terrorist involvement yet. ISIL in a Tweet claimed responsibility for it and there is a very aggressive ISIL chapter in the Sinai. But we really don’t know, and I think once the black boxes have been analysed, which they have recovered, then perhaps we will know more.”
Briefed by his transport minister, who had just arrived back from the crash site, Russian president Vladimir Putin offered condolences to victims’ families but no explanation.
“Without any doubt, everything has to be done to make sure we have an objective description of what happened. We have to know what happened and to react in the appropriate way.”
His team of investigators has widened its search in the Sinai Peninsula across 30 square kilometres. And as a second planeload of victims arrived in St Petersburg, the team vowed not to give up until all bodies are recovered.