To add to what's already been given, what you can do is right-click or Cmd-click on the folder which had the images that you removed from Lightroom and select 'Synchronize Folder'. When you do, make sure 'Import new photos' is checked. This will import the images back into your Lightroom catalogue, and show them together as 'last imported'. Now that you have them isolated you can select them all and delete them properly. If you have images from more than one folder, selecting the highest folder on the tree will import images in subfolders provided you have "Library/Show Photos in Subfolders" checked.
Mike.