Aviation and terrorism experts say the evidence so far points towards EgyptAir flight MS804 being brought down by a bomb.
The A320 disappeared from radar over the Mediterranean Sea, south of Greece, with 66 on board.
Egyptian and Greek officials earlier announced the wreckage had been found, but have since backtracked, saying pieces of plastic and lifejackets found 370km south of Crete weren't from the flight.
Egypt Minister of Civil Aviation Sherif Fathy said terrorism was the likely cause, a view backed up by Geoffrey Thomas, editor-in-chief of website airlineratings.com.
Radar shows the plane veered left then did a full circle heading right as it descended, but it just vanished from flight tracking websites, which Mr Thomas says is clear evidence of an explosion.
"The plane has exploded, and large pieces of it have veered left and right," he told Paul Henry on Friday.
"It may well be a hijacker or a terrorist got into the cockpit, there was a struggle, the plane veered left and right. That sort of course change would appear on the various flight-tracking websites… all we've got is a dead-straight line and it all of a sudden disappears."
Greg Barton, professor of Islamic politics at Deakin University, says it was a young aircraft -- only 13 years old -- flying in clear weather with an experienced crew. No mayday was sent, suggesting something happened very fast -- most likely an explosion.
"There could have been catastrophic mechanical failure, but even catastrophic failures give crews time to radio mayday," he said.
"With a modern aircraft, a reliable air crew and clear weather, it's most likely an act of terror."
Charles de Gaulle Airport has very strong security, particularly in the wake of Islamic State attacks in Paris, but Prof Barton says the plane was recently in Tunisia, Cairo and Eritrea,where a bomb may have been hidden by someone with access to the plane's less accessible areas, such as a luggage loader.
"It may have been a very small device… the size of a soft drink can," he explained.
"EgyptAir has a spotty safety record and it flies out of dangerous airports... terrorism is a case of choosing targets for symbolic value, but also opportunity."
Mr Thomas says the wreckage should be found soon, as the Mediterranean is not as large or deep as the southern Indian Ocean, where Malaysia Airlines flight MH370 is believed to have gone down.
"We're not talking about finding a wreckage weeks later when it's all drifted away. We should find it in a concentrated area, combined with fuel, oil, that sort of stuff on the surface of the ocean as well."