I wouldn't say it heavily implied that. I would still bet that it was Chaos, but while it was certainly stated by both Mathilde and Fooger that the Akkerman Pleasure Cult is a possible suspect, if Fooger had any actual evidence he would probably love to show it to us, and as Mathilde says right after the part you quoted it's not out of the question that whoever was actually responsible is taking the opportunity to pin it on the Akkermans:It's heavily implied, based on the social turn before last, that it was the doing of a Chaos cult within Marienburg.
So the presence of clues pointing both subtly to Marienburg and incredibly blatantly to Marienburg would have been the result of a plot that was, in fact, based within Marienburg, but which was attempting to frame the polity of Marienburg, probably with the goal to inspire war with the Karaz Ankor and even kick off War of the Ancients Round Two if the cultists got lucky and Ulthuan honored its treaty. That's why we were so confused, because it looked like a frame-job where both the framer and the framee were the same person, which made no sense. Assuming this is correct, it is a good thing we gave Belegar the recommendation we did, because while it hurts the Dwarven psyche to not have a clear target for a Grudge, Grudging the wrong target would have been far worse.
I also kind of disagree with the idea that there were hints heavily implying Marienburg was behind it. I feel like it kind of became accepted in the thread's memories that the material evidence was probably part of a frame job or something like that, but that actually doesn't make much sense. Besides the fact that the culprits had no way to know that Mathilde could or would go all CSI: Gold Order on then, all the material evidence really pointed to was that the perpetrators probably bought the super strong gunpowder that's currently the hot new thing in the underworld, and their ammunition was made in Kreutzhofen which is the crossroads of the vaults and thus highly trafficked by anyone heading to or from the Border Princes. Again, as Mathilde herself pointed out:"What other possibility do you have in mind?"
You'd been considering that since you left Marienburg. "Akkerman was part of the leading bloc of the Directorate," you say. "And they've been replaced by one of Fooger's choosing, who's forming his own bloc. Their guilt is certain, but the degree of it could very easily be exaggerated - if not now, then certainly by the end of the month. I don't doubt every major family in Marienburg is rifling through their own sins to see which ones can be convincingly buried in the rubble.
In conclusion, can we please follow up on the Skull River Ambush investigation this social turn?Someone of a mind to suspect Marienburg could draw a line directly south from Marienburg to Ubersreik for the powder, to Kreutzhofen for the equipment, to the Border Princes for the lackeys, and then to the Skull River for the ambush. Someone of a mind to clear Marienburg could quite reasonably point out that anyone in or around the Empire with money and contacts could have made this happen.