Deleting photos with no file

Somehow, I ended up with thousands of duplicate photos in my catalog. I can easily delete the duplicates from explore because they have unique file names which I can delete as a group. The problem is that they remain in the catalog but with no file attached. These photos are mixed with the originals so in order to delete them I have to pick each individually holding the control key then delete them. Is there any way to delete these unreferenced photos as a group. Thanks