The speaker refutes the different theories that were made in the passage to explain the missing crew of the ship Mary Celeste. The first possibility that there might have been a mutiny in the ship leading to the captain being killed and the crew does not hold. He says that the captain was highly respected among the crew and so a mutiny might not have occured. The second possibility,that the ship that discovered Mary Celeste playing a role behind the mysterious disappearance of the crew,also does not hold good because the prosecutors could not find any tangible evidence.
The speaker in turn provides another explanation. Alcohol barrels were being carried in the ship. Some alcohol might have leaked resulting in alcohol vapors being formed which in turn was a fire hazard. The captain, not experienced in transporting alcohol before , might have panicked and hence might have abandoned the ship with the crew. This is proved by the fact that no possessions were taken along. Later they might have perished in the journey.
Thus the speaker argues that neither of the theories as stated in the passage provide convincing explanations and that the one he suggested seems the most plausible.