The question of what caused EgyptAir Flight 804 to crash in the Mediterranean, killing all 66 on board, remains shrouded in confusion, speculation and conflicting statements. Here is a look at what is known so far and what questions remain unanswered.

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EXPLOSION OR NOT?

One of the primary questions is whether or not the plane was brought down by a bomb or some sort of mechanical failure. On Tuesday, two different Egyptian officials publicly disagreed on whether or not the available evidence indicated an on-board explosion. A senior Egyptian forensics official told The Associated Press that the condition of the human remains collected from the crash site so far indicated an explosion. Later however, the head of Egypt's forensic agency dismissed such talk, calling it "baseless."

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ON-BOARD FIRE?

The strongest indication of trouble on the flight so far comes from smoke detectors that went off and transmitted messages in the plane's final moments. France's air accident investigation agency said smoke was detected in multiple areas on the plane, with spokesman Sebastien Barthe telling the AP that such messages "generally mean the start of a fire." The cause however remains unclear for the French, with Barthe saying his organization was "drawing no conclusions from this. Everything else is pure conjecture." Industry publication Aviation Herald has reported that sensors detected smoke in the plane's lavatory, as well as a fault in two of the plane's cockpit windows in the final moments of the flight.

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CONFICTING STATEMENTS

While Egyptian officials publicly disagreed with each other Tuesday about whether the evidence so far indicated an explosion, there is also debate as to whether the plane suddenly flew erratically in its final moments before crashing. Greek Defense Minister Panos Kammenos has said it swerved 90 degrees to the left, then spun a full 360 degrees to the right as it plummeted and fell off radar. But the Egyptians refute this.

Ehab Azmy, the head of Egypt's state-run provider of air navigation services, says that the plane did not swerve or lose altitude before it disappeared. Azmy says that the plane was flying at its normal altitude of 37,000 feet when it vanished from radar. Egypt has also swiftly denied other reports over the plane's final moments — one that the pilots had sent a distress signal, and another that they had communicated with Egyptian air traffic control over plans to put out a fire on board.

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TERRORISM?

No group has claimed responsibility for the crash. The very day the plane went down, Egypt's Aviation Minister Sherif Fathi said that the possibility of a terror attack "is higher than the possibility of having a technical failure." The statement comes in stark contrast to Egypt's handling of last year's downing of a Russian airliner, when officials constantly denied the terrorism possibility, even after Russian investigators said a bomb had brought the plane down. President Abdel-Fattah el-Sissi, who eventually accepted the Russian assessment, has communicated quickly on the EgyptAir crash, cautioning against premature speculation. "There is not one scenario that we can exclusively subscribe to," he told Egyptian television. "All scenarios are possible."

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FLIGHT DATA

The search is still on for the plane's black boxes, which could be deep on the sea bed. There had been initial reports that they were found but Egypt later denied this. The first audio available from the flight indicates that all was routine when it checked in with air traffic controllers in Zurich, Switzerland, late Wednesday night, before being handed over to Italian air traffic controllers.

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PASSENGERS

Experts have also raised the theory of a rogue passenger taking over controls of the plane, or a struggle between pilots. But three European security officials say the flight's passenger manifest contained no known names on current terror watch lists. The lists are often used by both European and American security and law enforcement agencies. The passenger manifest was leaked online and has not been officially verified by EgyptAir.

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