Miller later became acting IRS commissioner, but was forced to resign last year after the agency acknowledged that agents had improperly scrutinized tea party and other conservative groups when they applied for tax-exempt status. Documents have shown some liberal groups were also flagged.
Investigators from the House Ways and Means Committee interviewed IRS technicians Monday. The technicians said they first realized that Lerner's emails were lost in February or March months before they informed congressional investigators, said a statement by two top Republicans on the Ways and Means Committee, chairman Dave Camp of Michigan and subcommittee chairman Charles Boustany of Louisiana.
The two lawmakers called on the Justice Department to appoint a special prosecutor to investigate the IRS, something Attorney General Eric Holder has declined to do in the past.
"It looks like the American people were lied to and the IRS tried to cover up the fact it conveniently lost key documents in this investigation," the statement by Camp and Boustany said. "The White House promised full cooperation, the commissioner promised full access to Lois Lerner emails and now the agency claims it cannot produce those materials and they've known for months they couldn't do this."
The IRS did not immediately respond to a request for comment.
"It is unfortunate that the IRS experienced equipment failure that resulted in several computers crashing and some email data being lost from Lois Lerner's hard drive between 2009 and 2011," said Rep. Sander Levin of Michigan, the top Democrat on the Ways and Means Committee. "But every equipment failure is not a conspiracy. The IRS has taken every step to restore the data, and has already retrieved the emails sent internally during that time period from non-impacted computers."
IRS Commissioner John Koskinen was scheduled to testify before the Ways and Means Committee on Friday. He was originally scheduled to appear next Tuesday, but the hearing was moved up because of a scheduling conflict. The House Oversight Committee has subpoenaed Koskinen to testify at a rare evening hearing on Monday.
The two House committees and the Senate Finance Committee are investigating the IRS over its handling of tea party applications from 2010 to 2012. The Justice Department and the IRS inspector general are also investigating.
Congressional investigators have shown that IRS officials in Washington were closely involved in handling 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.
If anyone outside the agency was involved, investigators were hoping for clues in Lerner's emails.
Lerner's computer crashed in the summer of 2011, depriving investigators of many of her prior emails. Flax's computer crashed in December 2011, Camp and Boustany said.
The IRS said Friday that technicians went to great lengths trying to recover data from Lerner's computer in 2011. In emails provided by the IRS, technicians said they sent the computer to a forensic lab run by the agency's criminal investigations unit. But to no avail.
The IRS was able to generate 24,000 Lerner emails from the 2009 to 2011 period because Lerner had copied in other IRS employees. Overall, the IRS said it is producing a total of 67,000 emails to and from Lerner, covering the period from 2009 to 2013.
The IRS said Friday more than 250 IRS employees have been working to assist congressional investigations, spending nearly $10 million to produce more than 750,000 documents.
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