Did you read the document? There is no doubt, as there was on the Iowa, about the source of this fire. It doesn’t say an exact number, but the fire investigation found about four or five infernal devices designed to start a fire - they weren’t built into the ship. There is no doubt that someone started the fire but there is some doubt that Mays was that person, thus the search. A trial requires means, motive, and opportunity and all three appear to be there. It strikes me that the investigation is looking for an electronic trail to find out who moved the bottle marked by the fire investigation.
There really is only the slightest comparison to the Iowa in that they were both ships and both had fires on board.