Problems with Mac's Trash

"Was the backup folder a Timemachine folder? Those folders are weird.

If you deleted it from an external HD it will be in the trash can of the external hd. It should vanish from the trash can when you remove the external disk.

I think you might have to reformat the external disk to get rid of a Timemachine folder, whether in trash or otherwise."

"Take a look at your external drive, via the terminal:

Last login: Tue Sep 22 07:42:31 on console
cd dhcp105-37:~ Ben$ cd /Volumes/External_Drive
dhcp105-37:External_Drive Ben$ ls -la
total 954440
drwxrwxr-x@ 29 Ben staff 1054 Aug 18 15:43 .
drwxrwxrwt@ 6 root admin 204 Sep 22 07:43 ..
-r-------- 1 root staff 16 Aug 5 2008 .001ff3584d0c
-rw-rw-r--@ 1 Ben staff 21508 Sep 16 14:56 .DS_Store
drwx------ 3 Ben staff 102 Aug 5 2008 .Spotlight-V100
drwxrwxrwt@ 3 Ben staff 102 Oct 1 2008 .TemporaryItems
d-wx-wx-wt 3 Ben staff 102 Sep 11 13:39 .Trashes
-rw-r--r--@ 1 Ben staff 227377 Apr 9 15:36 .VolumeIcon.icns
-rw-r--r-- 1 Ben staff 0 Aug 5 2008 .com.apple.timemachine.supported
drwx------ 88 Ben staff 2992 Sep 22 07:49 .fseventsd
drw

Please note the .Trashes that exists on the external drive. Take a look at your external and see if the folder is in there. If so, then a rf command from that folder should work.

Time Machine backup folders are indeed different, but my understanding is that they can be deleted like any other folder/file. The issue is that since Time Machine backups are hard linked files, that when you delete it from one backup set, you maybe deleting from multiple sets at the same time."