I had problem emptying trash folder on my Mac because most of the files were locked. After a few tries on google, I found that you can delete locked files by either log in as admin and issue delete command on each locked file. If you want to delete multiple locked files say a whole folder, you can do this easily by move all those files into trash then hold Shift+Option key when you empty trash.
Be careful when you delete these locked files though. It's likely that these files are locked for good reasons.
