How to delete in iTunes for Mac some PDF files, previously synched with iPhone and then deleted from it?

Question

A while ago I synced some PDF files from my iTunes to my iPhone.  I've deleted those PDF files from my iPhone recently but now i'm trying to delete them from iTunes but can't.  How can this be done?
P.S. Tried to select/highlight them (OK) and then to delete with cmd+Backspace - doesn't work 

Answer 1

I am sure the URLConnection.defaultUseCaches is set before it is connected otherwise I should catch an IllegalStateException on conn.setUseCaches(false).
        try
            URL url = new URL("jar:file:/C:\\a.jar!/a.gif");           
         URLConnection conn = url.openConnection();
           conn.setDefaultUseCaches(false);
         conn.setUseCaches(false);
            Icon icon = new ImageIcon(url);
            System.out.println("icon size ? " + icon.getIconHeight());
            url.openConnection().getInputStream().close();
            System.gc();
         System.runFinalization();
            File file = new File("c:\\a.jar");
            while (file.exists())
                file.delete();
                try
                    Thread.sleep(10);
                catch (InterruptedException ignored)
            System.out.println("file deleted.");
        catch (Throwable t)
            t.printStackTrace();