deletion of images from disc.

Right click the folder in Lightroom and choose Synchronize folder. In the dialog that appears, make sure that Show import dialog before importing is checked.

The removed files will appear in the Import dialog, and you can now identify them and delete them in the Finder – or import them, if you prefer.

Since you only removed them from LrC, the images remain in the folder on your hard drive where they were imported. They are no longer part of your LrC catalog. It will be necessary for you to use Finder to browse to that folder, locate the images and use Finder to delete those images. You probably have read or watched tutorials warning not to do anything outside of Lightroom. However, in this case you are safe to do so because those images have been removed from your Lightroom catalog and are no longer being tracked by the program.

Remove (from LR) does remove it from LR but doesn't move the document. It is simply removed from the catalog. They remain in the location they did prior to using that command. 

To get them back in the catalog, just import them back (you can use the Contextual menu: Sync Folder and they should reappear in the Import dialog if so set they come back where they were). 

Delete does just that, moves to the trash while removing the photos from the catalog or course.