Internal Revenue Service officials testifying before Congress in the probe of the agency’s harassment of conservative organizations have acted shocked – shocked – at suggestions a coverup is occurring.

But the foul odor of attempts to cover up criminal behavior at the IRS has done nothing but grow stronger.

A few weeks ago, lawmakers seeking emails from former IRS official Lois Lerner were told many of them were not available. Lerner, who headed the division responsible for mistreating conservative groups, had suffered a computer hard drive failure, agency officials said. Many emails were lost, and there was no backup for them.

But some of Lerner’s emails did make it to Congress. In one she sent to fellow IRS employees in April 2013, Lerner said this: “I was cautioning folks about email and how we have had several occasions where Congress has asked for emails and there has been an electronic search for responsive emails – so we need to be cautious about what we say in emails.”

Reasonable people may wonder why IRS officials needed to be cautious – if they were doing their jobs and obeying the law. Some also may wonder whether Lerner previously had not heeded her own advice, then needed a way to keep certain emails from coming to light.

This one stinks to the high heavens. Members of Congress should begin considering appointment of a special prosecutor.