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But specialists, viewing her instructions as too broad, again started to use policy-based criteria in January 2012. Republican lawmakers raised questions about reports of intense and laborious scrutiny of conservative groups seeking tax-exempt status, which prompted the audit.

The IRS changed its criteria once more in May 2012 to bring it in line with Treasury Department regulations.

Astonished by this month’s revelations, lawmakers held hearings in quick succession before the House Ways and Means Committee, the Senate Finance Committee and the House Oversight and Government Reform Committee.

Ms. Lerner said she did nothing wrong but refused to answer any questions from the House oversight committee Wednesday, prompting a rebuke and threats to haul her back for another hearing.

“After consulting with counsel, Chairman Issa has concluded that Ms. Lerner’s 5th amendment assertion is no longer valid,” committee spokesman Ali Ahmad said Thursday in an email. “She remains under subpoena, [and] the Committee is looking at recalling her for testimony.”

House Minority Leader Nancy Pelosi, California Democrat, said Thursday that she did not know Ms. Lerner’s motives but thought the reluctant IRS official should have testified.

“I do think the American people deserve answers,” Mrs. Pelosi said Thursday. “I wish that she would have provided them.”

Who knew what?

Officials with the Treasury Department and Obama administration have denied inside knowledge of what was going at the IRS.

The White House has edited its narrative of what top staff knew about the pending audit report.

At first, White House spokesman Jay Carney said Mr. Obama learned of the inappropriate targeting through news reports. But he didn’t volunteer any details about high-level staff who had warning about the audit.

He told reporters last week only that White House counsel Kathryn Ruemmler knew about the IRS probe the week of April 22, and later specified it was April 24. He waited until days later to reveal that several senior White House aides, including chief of staff Denis McDonough and deputy chief of staff Mark Childress, knew that same week.

Even though his top aides knew, he said, they never informed the president or discussed it with him until he learned of the targeting May 10 when it broke in the news.

On Capitol Hill, lawmakers admonished Mr. Shulman for failing to recognize that something was “rotten in [his] shop” during his tenure from 2008 to November 2012.

Mr. Shulman testified that he was reluctant to step into the fray or update Congress on suspected wrongdoing while the inspector general was looking into the problem.