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WASHINGTON (AP) — The investigator who wrote a scathing report about the Internal Revenue Service targeting conservative political groups is heading back to Capitol Hill as a key House Democrat says his committee's investigation has found no evidence of political bias at the agency.

IRS inspector general J. Russell George is to testify Thursday before the House Oversight and Government Reform Committee, along with two IRS workers who have been interviewed as part of the committee's investigation.

George has been criticized by some congressional Democrats who say his report failed to mention that some liberal groups were targeted, too.

Rep. Elijah Cummings, D-Md., released a memo Tuesday saying that interviews with 15 IRS employees and reviews of thousands of emails reveal no evidence of political bias by IRS workers. The memo said there is also no evidence that anyone outside the IRS directed the targeting.

Cummings is the ranking Democrat on the oversight committee. The oversight committee is conducting a bipartisan investigation of the IRS. The investigation, however, has been marked by partisan sniping between Cummings and committee Chairman Darrell Issa, R-Calif.

The IRS has been under siege since the agency acknowledged in May that agents had improperly targeted conservative groups for additional scrutiny when they applied for tax-exempt status during the 2010 and 2012 elections. George's report blamed ineffective management for allowing the practice to continue for more than 18 months, delaying hundreds of applications for more than a year.

George's report, however, did not indicate that Washington initiated the targeting of conservative groups.

Also testifying at Thursday's hearing: IRS agent Elizabeth Hofacre, who works in the agency's Cincinnati office, and Carter Hull, an IRS tax law specialist in Washington who recently retired.

Hofacre and Hull worked together processing some of the earliest tea party applications in 2010, according to a transcript of Hofacre's interview with congressional investigators.

Since the revelations were made public, three congressional committees and the Justice Department launched investigations and much of the top leadership of the IRS was replaced.

The agency's new acting head, Danny Werfel, is scheduled to testify Wednesday at a hearing before the House Small Business Committee.

In other IRS news, Werfel said Tuesday he was canceling a planned furlough day planned for Monday. The agency had announced five furlough days, in which the entire agency shuts down, because of automatic spending cuts enacted this year.

Werfel told employees in a memo that other cost-cutting measures have enabled the agency to cancel the furlough day. Werfel announced last week his intention to cancel nearly $98 million in employee bonuses.

The IRS has already furloughed workers three days this year. Another furlough day is scheduled for Aug. 30. Werfel said he has not yet determined the status of that furlough day.