"With two subpoenas and three preservation orders in place, under Mr. Koskinen's watch the IRS destroyed 422 backup tapes containing potentially 24,000 emails relevant to the IRS targeting of conservative organizations," Jordan said. "This is unacceptable."

In recent congressional testimony, Koskinen admitted that the emails were irretrievably gone; that the "backup tapes" had been erased; and that Lerner's hard drive was apparently destroyed in an aggressive act of recycling. With that settled, Koskinen expressed his "hope that the investigations ... can be concluded in the very near future."

Tempers flared in a House Oversight and Government Reform Committee hearing Wednesday, with members on both sides of the aisle castigating the Internal Revenue Service for targeting conservative groups with special scrutiny, and then hiding the practice from Congress.

Internal Revenue Service officials denied for months the targeting of conservative political groups for reviews of their tax exempt status. With investigators poised to expose the chilling operation, a high-ranking IRS official acknowledged it late last week and apologized for it. The agency blamed low-level employees, saying no high-level officials were aware. That appears to be untrue. The Associated Press reported Saturday that senior IRS officials knew agents were targeting tea party groups as early as 2011.