well it could have been the same as devils will.In John 10:10 Jesus said the devil comes to steal, kill, and to destroy.
So when Cain killed Able this was obviously the devil's will that Cain was fulfilling.
If someone claimed it was God's will for Able to be killed by Cain then this would be claiming Jesus lied.
But I can't see that it was the active will of the devil inside of him.
The active will of the power of death was in him
The reason why I don't see it was the active will of the devil inside of him.
In my book there is absolutely no way God would say to the devil you can rule over sin