Personally, I found that Sdelete did not work on files that were erased and in the NTFS MFT. Only Eraser worked when erasing free space.....
http://sourceforge.net/project/showfiles.php?group_id=37015
fwiw....
Another utility available on Source Forge will allow you to delete ALL of the files in free space and the entries that are flagged as deleted in the MFT. Recuva will no longer list them. It is Eraser 5.86. I tried others (of note PGP and Sdelete) to no avail. Eraser worked for me.
http://sourceforge.net/project/showfiles.php?group_id=37015
Cheers!