1.   A week ago, the FBI confirmed that its lab and another independent laboratory had detected a microscopic trace of explosives.

2.   Early in the investigation, officials found microscopic chemical traces of explosives in the wreckage, leading them to suspect a bomb.

3.   Officials said that could possibly explain the microscopic traces of explosives that were found on pieces of the wreckage.

4.   Some evidence, including microscopic traces of explosives, seemed to back up the instincts that a bomb or missile was involved.