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Washington • The Internal Revenue Service said Friday it has lost a trove of emails to and from a central figure in the agency's tea party controversy, sparking outrage from congressional investigators who have been probing the agency for more than a year.

The IRS told Congress on Friday that it cannot locate many of Lois Lerner's emails before 2011 because her computer crashed during the summer of that year.

Lerner headed the IRS division that processed applications for tax-exempt status. The IRS acknowledged last year that agents improperly had scrutinized applications for tax-exempt status by tea party and other conservative groups.

"Today's admission by the IRS that they cannot produce Lois Lerner's emails is an outrageous impediment to our investigation," said Sen. Orrin Hatch, R-Utah, the leading Republican on the Senate Finance Committee. "Even more egregious is the fact we are learning about this a full year after our initial request to provide the committee with any and all documents relating to our investigation."

The Senate Finance and House Ways and Means committees have vowed detailed probes of the IRS over its handling of tea party applications from 2010 to 2012. The Justice Department and the IRS inspector general also are investigating.

Congressional investigators have shown that IRS officials in Washington were involved closely in the handling of tea party applications, many of which languished for more than a year without action. But so far they have not publicly produced evidence that anyone outside the agency directed the targeting or even knew about it.

The IRS was able to generate 24,000 Lerner emails from 2009 to 2011 because Lerner had sent copies to other IRS employees. The agency said it pieced together the emails from the computers of 83 other IRS employees.

But an untold number are gone.

The IRS said in a statement that it has gone to great lengths cooperating with congressional investigations, spending nearly $10 million to produce more than 750,000 documents.

Overall, the IRS said it is producing a total of 67,000 emails to and from Lerner, covering the period from 2009 to 2013.

Tribune reporter Matt Canham contributed to this article.