Cian/Fee.
No idea as to the who or why, unfortunately, but I've some details on the 'how' (which may as of yet lead to 'who'?). They used some sort of flash bomb or electric shock guns, presumably to subdue their victims. Cogs and gears were present at the scene, proof of some mechanical work. Cheap materials, cobbled together from alloys sold around the Tenements. They knew their way around machinists' work, it seems.