As clues come together, aviation analysts try to determine what cause the Russian airliner to crash

Just days after a Russian airliner crashed in Egypt shortly after departure, clues are emerging and theories are taking shape as aviation analysts try to understood what happened.

While ideas of what could have caused the incident include an explosion, a fire on board, or a non-standard emergency, a new CNN report shines light on the difficulties officials are facing in determining a singular cause.

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According to the report, air traffic controllers didn’t receive any distress calls before the plane – headed to St. Petersburg, Russia – went down, just 23 minutes into the flight. However, the website Flightradar24, which tracks aircraft globally, claims to have received data from the plane that points towards sharp altitude changes and a marked decrease in ground speed before losing signal.

Satellite data from the U.S. military reports a midair heat flash from the plane, leading some to believe there may have been an explosion, one U.S. official told CNN. While intelligence analysis has confirmed that a missile was not responsible for the crash, there may have been a disastrous in-flight incident, the U.S. official continued, adding that the possibility of a bomb has not been ruled out.

However, while a bomb is still an option, Russian state media has said that no traces of explosive devices or materials have been found in the debris as of yet.

Chris Owen, an explosives expert from Alford Technologies, told CNN that ruling out an explosive simply because no evidence of one had been found, will be difficult.

“If a bomb is ruled out, it will likely be because another cause has been found,” he continued, adding that while explosive residue could be found during lab testing, it would be faster to determine if an explosive was on board by considering the damage to plane parts.

Although examining plane parts could help decipher if an explosive was used, a medical source added that the bodies were intact and showed no major burns.