Responses
He always has that small weapon with ruby on it that was given by the King. Also, I everyone there is on the side of the older prince, so they must've known the plan and doesn't really care. They're the only ones who came there as "witnesses". So, if they tell it to others, others would believe them. Specially when people know how strong he is. Although, there's no reason for him to even do that, I'm sure the older prince would make up a fake reason. Simple as that. Don't blame the author.
everyone**
that "assassination attempt" on the king didn't make any sense at all. Latio didn't even have a weapon(or did he?). And there was barely enough time to attack and return back to his position at all. (っ°Д °;)っ
The author just randomly put it there for the sake of the plot.（/TДT)/