The EgyptAir plane that crashed into the Mediterranean Sea on Thursday was emblazoned with the words "we will bring this plane down" two years ago.
The chilling message written in Arabis on the A320's underside by aviation workers in Cairo, prompted a major security upgrade at the airline.
Employees with particular political leanings were fired, crew searches increased and extra in-flight security guards added.
The measures may have all amounted to nothing however, with terrorism still considered the most likely reason for Thursday's crash as the A320 flew from Paris to Cairo.
All 66 people on board were killed, including three in-flight security guards and a British-Australian citizen, Richard Osman, 40.
Debris from the aircraft recovered from the Mediterranean Sea included luggage, seat belts, a lifejacket and human remains.
But salvage crews were yet to find the fuselage and the all-important black box recorders.
The cockpit voice recorder and flight data recorder should reveal whether the A320's plunge into the water was in fact a mechanical issue, or something more sinister - like a bomb.
Messages sent from the plane's automatic detection system indicated they were a series of smoke alerts issued just before the crash.
Spokesman for France's Bureau of Investigations and Analysis, Sebastien Barthe, warned against reading too much into the alerts.
"These are not messages that enable us to interpret anything," said Mr Barthe.
"If there is smoke, it means there is potentially a fire somewhere but it doesn't tell us where the fire is, and it doesn't help us establish whether it is something malevolent or something technical."
But former pilot turned author, Peter Stuart Smith said it would have had to be a very big fire to bring the plane down within three minutes of the smoke alerts being issued.
"The most likely explanation in my view is a large bomb in the cargo hold, that could decompress the aircraft immediately and render some or all of the controls inoperative," he said.
"If there was a mechanical issue or even a fire, the crew should've had time to make a mayday call."
He said the main flaw in his theory was the security at Charles de Gaulle Airport.
"The aircraft was on its fifth flight that day so it is at least possible that it might have picked up hold goods destined for Egypt in another country with less comprehensive screening standards," Mr Smith said.
"These could have remained on board the aircraft while it was on the ground in Paris."
Security guards did not monitor baggage handlers who load the plane's hold, he revealed.
During stopovers, the unarmed guards were responsible for searching workers who clean the planes and check the credentials of crew members and employees who board.
However in Paris, EgyptAir security officials were not permitted to search cleaners.
No terrorist group has claimed responsibility for the crash however a message purporting to come from Islamic State urged attacks on the United States and Europe during the Islamic holy month of Ramadan starting in early June.
"Ramadan, the month of conquest - get prepared so that you can make it a month of calamity on the nonbelievers anywhere," said the message posted on Twitter accounts that normally publish IS statements.
There was no mention of the EgyptAir crash.
Meanwhile, Egypt's President Abdel-Fattah el-Sissi said a submarine belonging to his country's Oil Ministry was headed to the site of the crash to join the search for the black boxes, adding Egypt was jointly investigating the crash with the French government.
"It is very, very important to us to establish the circumstances that led to the crash of that aircraft," he said in comments broadcast live on Egyptian TV channels.
He said the submarine, which has the capacity to operate at a depth of 3000 metres below the surface, left for the site on Sunday. He gave no further details.
Making his first public comments since the crash of the Airbus A320 while en route from Paris to Cairo, el-Sissi said it "will take time" to determine the exact cause of the crash.
He thanked the nations that have joined Egyptian navy ships and aircraft in the search for the wreckage and started his comments with a minute of silence in remembrance of the victims.
El-Sissi also cautioned the media against premature speculation on the cause of the crash.
"There is not one scenario that we can exclusively subscribe to ... all scenarios are possible," he said.