1.   Instead, he said, three theories are being investigated, a bomb, a missile attack and a catastrophic mechanical malfunction.

2.   When the ordeal is over, you flip a switch and invariably one of the strands that worked when they were tested earlier has suffered a catastrophic malfunction.

3.   In addition to a missile attack, the two other main theories are a bomb or a catastrophic mechanical malfunction.

4.   Investigators believe the plane was either downed as a result of a missile attack, a bomb or a catastrophic mechanical malfunction.

5.   The three main theories being pursued are that the explosion was caused by a bomb, a surface-to-air missile or a catastrophic mechanical malfunction.