If your files weren't stored on your Mac, they won't land in
… but instead on the drive itself, which is accessible here:
501 is the default user ID of your Mac OS X user account. You can try to manually
rm the files from there.
cd '/Volumes/La Cie/.Trashes/501' ← this will go to the Trash on your external drive
ls ← this will list all files in the Trash
rm some-file ← this will remove the file named
some-file from the Trash
If that fails, the problem is that the files aren't owned by your user account. Therefore you can try to prefix
sudo, which will try removing the file with root permissions.