So - what started the final raid?

I might be missing something....
.... so the king ordered the raid, which ended the ambitious Minister's grasp for the throne.
And the investigation helped start this?

Who the hell were the guys that attacked the old detective at the (roughly) half of the movie?

Does anybody else have the impression that these key plot milestones didn't have the attention they deserve?

And - why did the Minister said "Was it you?" to the black swordsman?
Did the swordsman do something that lead to their downfall?