There probably wasn't an actual murderer. In earlier chapters it was hinted that the previous king had some kind of deadly disease, and it was only a matter of time anyways. I think he just had an attack from the disease and due to how he treated people no one went for help.
man this country feels kinda dumb, why not practice with guns away from the town and why would soldiers be hated by their own country that and what technology do they have i saw a train and bayoneted rifle but the fortresses kinda look like they need to be saved by the wing hussars, but the food looks good.
at the beginning was explained this... he is not small he is "half-something" due to a meridian problem, don't really remember the details now, so I suppose that he did something and now he's normal sized