If I were to be suspicious, I would first suspect those who oppose drilling and desire the economy to shift toward other energy sources. Such an accident could generate sympathy and money to force the economy to alter paths.

That would be my initial most suspect group right there too.

I would guess that wasn't this an op in the sense that the rig suffered some assault by some outside force...like scuba dudes planting bombs on it...I just don't see that and also I think Naval assets to protect rigs would be a waste for this reason.

Some states would gain for sure, but would they sponsor such an attack from the inside for either monetary or idealogical reasons?....I would think the risk wouldn't be worth the reward for that...cause if they were caught?....the response would be harsh whether it was military or economic....so if this was sabotage I will go with your first impression too...some group that wouldn't be associated directly with a nation state.