No, it's not accidental. It's the result of an intentional act on the part of the alleged perpetrator. The perpetrator is free to raise that as a defense in court but I don't see it flying, unless the jury is made up of animal haters.
As to the laws, I don't know what NC's laws are on hazardous waste. Even if it isn't illegal to leave open containers of hazardous waste laying around your yard, that doesn't mean it's not a violation of animal cruelty laws to do it if you are trying to kill animals.

