Hidden ‘in use’ file preventing Office MAC 2011 uninstall
If sudo rm didn't delete it, then maybe it somehow got the schg flag set?

You could try this:

    sudo chflags noschg /Users/bob/.Trash/nasty.file.ext

    sudo /bin/rm -f /Users/bob/.Trash/nasty.file.ext


As I mentioned in the comments, you could also try moving the file to /tmp/ and rebooting, since that usually clears out the /tmp/ but I have a sneaking suspicion that isn't going to help in this case.