Deleted files on NFS if still open are renamed in place to a funny .nfs* name, and other open deleted files used to go to /mount-point/lost+found/ You might be able to see them using lsof, and kill...
They may be in deleted files. files which are deleted while still in use, will remain on disk until the files are closed. If someone naively deletes files to free up space, this may cause a problem...