It could have been a fire, a bomb, a cascading electrical failure — or something else altogether.

The first hard evidence about what brought down EgyptAir Flight 804 last week — a string of seven error messages sent automatically minutes before the Airbus A320 plunged into the Mediterranean — has done little to narrow down what happened, according to aircraft specialists and accident investigators.

“Until they get the data recorder back, it would be hard to come up with an idea,” said Michael Barr, an accident investigation instructor at the University of Southern California, said

An Egyptian forensics investigator said Tuesday that body parts retrieved from the sea so far have been small. That might suggest some sort of explosion, he said, though bodies can also be ripped apart when an aircraft disintegrates following a structural failure or hits the ground or sea at high velocity.

Uncertainty over what caused the May 19 crash is delaying any response by policymakers, whether it be a hunt for a terrorist who planted a bomb or revising safety procedures to prevent similar types of accidents in the future.

The error messages that emerged over the weekend include two separate alarms indicating smoke, suggesting there could have been a fire before the flight from Paris to Cairo plunged into the water, killing all 66 aboard. One of the alarms reported that smoke had been detected directly beneath the cockpit where the plane's computers and avionics equipment are located. The other was in a lavatory.

Other alerts showed unspecified problems with flight computers.

The error messages were confirmed by the French accident investigation agency BEA over the weekend after they were first reported on the Aviation Herald website.

Two people who are familiar with the Airbus A320 design said while the data may point to a fire on the plane, that didn't rule out other possibilities. Some type of bomb or incendiary device might have triggered the alerts, they said. A widespread electrical failure was also conceivable. At this early stage in the investigation, they said, the cryptic alerts don't rule out much.

The timing of the alerts is also puzzling. They began at 2:26 a.m. local time and continued for three minutes.

In previous cases in which a bomb or explosion destroyed an airliner, the electrical systems failed almost instantly instead of over several minutes.

By contrast, fires that have led to crashes on large planes have typically taken much longer to take them down. Even in cases in which fires moved more quickly, such as the 1996 crash of a ValuJet plane near Miami, pilots were able to make radio calls alerting air-traffic controllers to the crisis and attempt an emergency landing.

In the EgyptAir crash, there were no such radio calls from pilots, according to Ehab Azmy, the head of Egypt's National Air Navigation Services.

If a fire destroyed those computers, the plane would be difficult to fly, they said. However, the Airbus is designed to stay aloft even if all its computers fail, so it should have been possible to continue flying.

Debris from the plane has been found about 180 miles off the Egyptian coast and the Egyptian government has sent a submarine to the scene in an attempt to locate wreckage, particularly the two crash-proof recorders.

Until more concrete data from those recorders can be analyzed, it doesn't make sense to pick one theory over another, according to Tony Fazio, who headed the U.S. Federal Aviation Administration's accident investigation office for five years before starting a consulting company.

“That's always our bottom line,” Fazio said. “Anybody with any credibility will tell you that it's just way too soon.”