It's more like the prince provoked Chang Hai to make a confession under coercion. That gave him the reason to attack the prince who in turn used the sword to kill him. It appears like the King used his own son to be the executioner to exonerate himself from meting out punishment to his brother-in-law.
![Felix "Unfair" | [Stray Kids : SKZ-PLAYER]](http://i.ytimg.com/vi/Oswujxm2Ag0/mqdefault.jpg)
It's more like the prince provoked Chang Hai to make a confession under coercion. That gave him the reason to attack the prince who in turn used the sword to kill him. It appears like the King used his own son to be the executioner to exonerate himself from meting out punishment to his brother-in-law.