Justifiable homicide is not murder. The only crime they committed was not reporting the death to the police... At least that would be the common law (western legal philosophy) answer to it. I can't say for Japan though.
Honestly, they probably could've gone to the police and been safe on self-defense, but not so much with the cutting up of and hiding the body. Well, I'm sure nothing bad will happen.
Ay~! We're caught up! Based on when chapter 15 came out, I think chapter 16 might be within a week or so? But Tsukinowa-sensei might've been busy with the volume 2 release so who knows. I'll work on it as soon as it comes out though, because I love this manga. Hopefully our girls can enjoy the rest of their trip in peace before shit inevitably goes down again.