Re: OPEN Mass Grave
That was my first impression too.
When the Others heard that Ben was taking Locke to see Jacob, they had a look of shock/fear. Maybe this is not the first time Ben has taken someone to see Jacob and killed them afterward. Maybe this is why Alex provided Locke with a weapon. Maybe it was to protect himself from Ben (who by her own admission, manipulates people into thinking something was their own idea, when it was Ben's plan all along.)
No need to cover it up when there will just be a need to use it again.