How to Delete a file stored in the Document Catalog?

Today we had a user accidentally publish a receipt to the "Document Catalog" in the Internet Expenses module.  They accomplished this by accessing the expense report, clicking the attachment and then clicking the "Publish To Catalog" icon on the far right.  The user obviously wants to delete this file from the Document Catalog so that it is no viewable by other users.  How do we go about deleting the file? Or how do we even query or access files in the Document Library? Thanks in advance.