A Brazilian ship searched for bodies and clues in debris from Air France Flight 447 yesterday, while the chief investigator said that the world might never learn why the Airbus with 228 aboard plunged into the Atlantic.

The naval vessel was the first to arrive at the floating wreckage, which was found by Brazilian and French spotter aircraft, scattered widely over an area about 745 miles (1,200km) northeast of the coastal city of Recife.

French authorities confirmed that seats, plastic and sections of aluminium on the surface were from the Airbus A330 that came down early on Monday while flying through severe storms from Rio de Janerio to Paris. The discovery dashed hopes that passengers could have survived.

As ships steamed to the scene, reports of a recent bomb threat to an Air France South American flight stirred speculation that an explosion could have brought down Flight 447. Airline sources said that the company attached no significance to the false alarm, which involved an aircraft at Buenos Aires airport on May 27.

Last night Nelson Jobim, the Brazilian Defence Minister, also ruled out an explosion. A long fuel slick found at the crash site “means that it is improbable that there was a fire or explosion”, he said.

President Sarkozy and Carla Bruni, his wife, attended an all-faiths service at Notre Dame cathedral in memory of the victims of the world’s worst air disaster since 2001. Dozens of Air France personnel attended in uniform, mourning their 12 colleagues. The missing include 61 French, 59 Brazilians, 26 Germans and 5 Britons, including an 11-year-old boy who was returning to school after a half-term break visiting his parents in Rio de Janeiro.

Friends and classmates at Clifton College Preparatory School in Bristol where he was boarding paid tribute to Alexander Bjoroy yesterday. His parents and nine-year-old sister were returning to Britain.

A poem by Ademar de Barros, a Brazilian, was read to the grieving families and friends at the Paris service. The poet addresses God, saying: “Why did you leave me alone at the worst moment of my life?” God answers: “The days when you see only one set of footprints in the sand are the days that I was carrying you.”

In Paris, Paul-Louis Arslanian, the chief of the French accident investigation bureau, said that it would take a long inquiry to find the cause of the disaster.

The aircraft’s “black box” flight recorders would be invaluable but it was possible that they might not be found because they would lie 12,000ft down on an ocean bed that resembled mountains. Early next week a French deep-sea research vessel and robot submarine are to try to trace and retrieve the recorders, which should be transmitting homing signals. No “black box” has been recovered from such a depth.

Even with the recorders, investigators might never be able to solve the mystery of Flight 447, said Mr Arslanian. “I cannot rule out the possibility that we might end up with a finding that is relatively unsatisfactory in terms of certainty,” he added.

He did promise to report any solid indications as soon as they were found, “whatever the consequences”. Speculation continued to focus on theories that severe tropical storms were behind a catastrophic failure in the all-electronic aircraft, which appeared to have broken up before hitting the ocean. Leaks from Air France prompted theories that ice could have blocked the aircraft’s external air probes, confusing its computerised flight system. The last word from the pilots, half an hour before the crash, reported bad weather in the area.

Air France said earlier that the aircraft had been struck by lightning. They ruled out terrorism but later retracted the remarks. Sabotage was not being ruled out.

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