The American claim, made in unsourced leaks from the crash inquiry, has caused a nasty argument between Egypt and the US, and the new caution may simply reflect a desire to calm this row. But it is also clear that some of the "evidence" is less than solid, and was leaked before it had been checked. There are also signs of internecine warfare between different US agencies.
The head of America's National Transportation Safety Board, Jim Hall, condemned the leaks, saying they had created "a virtual cyclone of speculation". He added that "some unidentified sources have led some in the media to speculate on undocumented information", and went on to make pointed references to the FBI, the board's partner in the investigation. He said he believed that the crash "might be the result of a deliberate act", but added that there had been "headlines with information that is just flat wrong".
The issue has become not just an argument about what caused the flight from New York to Cairo to crash, but a dispute about motives and prejudices. The Egyptians believe the US is trying to protect Boeing, and that it automatically suspects Muslims of being guilty of reckless acts if not terrorism. The Americans privately believe that the Egyptian government is trying to protect its national carrier.
The American theory turns on a few facts whose interpretation is disputed. The cockpit voice recorders apparently show that the aircraft's captain, Ahmed al-Habashi, left the flight deck, leaving the relief co-pilot, Gamil al-Batouti, at the controls. He had been reported to have said "I made my decision now", before repeating a Muslim prayer variously translated as "I put my faith in God's hands" or "I depend on God".
But yesterday, an unnamed official told news agencies that Mr Batouti did not say "I made my decision now". Earlier in the week, CNN reported that two different American officials had disputed whether the quote was recorded. The official described the error as an "innocent mistake'' even though it is one factor which has led the English-speaking media, with little evidence, to label Mr Batouti a suicidal killer.
The US investigation has been led by the National Transportation Safety Board and the Federal Bureau of Investigations, two organisations that have clashed in the past and appear to be having a rough time now. If the crash is regarded as a criminal act, the FBI would take over.
Egyptian officials said there was now consensus that the crash would not be handed over to the FBI. "A political agreement was reached with the US side that the file will remain with the National Transport Safety Board,'' said Murad Shawki, head of aviation safety at the civil aviation authority, as he returned to Cairo.
Egyptian officials were examining the voice recorder, the transcripts from which convinced US investigators that the co-pilot deliberately put the aircraft into a steep dive.
So far, the Egyptians are far less convinced, though unlike their US counterparts they have not been prepared to speculate anonymously to the press about their own theories. The truth probably lies in the fragments of wreckage spread across miles of the seabed, and it may never be clear to everybody's satisfaction. The salvage operation, off Nantucket island, Massachusetts, continues.