Empty Securely only overwrites your trashed items so they can't be recovered. Check this article http://www.macobserver.com/tmo/article/Using_Secure_Empty_Trash/
If you can't empty the Trash or move a file to the Trash
For example, this message might appear when you try to empty the Trash: "The operation could not be completed because the item '(item name)' is locked."
First, try holding the Option key as you choose Empty Trash from the Finder's File menu.