Conversation so far:
what was the tax evasion with Ernie Kovacs about?
A frequent critic of the U.S. tax system, Ernie Kovacs owed the Internal Revenue Service several hundred thousand dollars in back taxes, due to his simple refusal to pay them.

Question: how did they find out?
Self-contained rewrite: how did the IRS find out about Ernie Kovacs's tax evasion?