"You've never heard of a computer crashing before?" White House spokesman Josh Earnest said on Monday, when a reporter asked if that was a "reasonable explanation."
"I think it's entirely reasonable, because it's the truth and it's a fact, and speculation otherwise I think is indicative of the kinds of conspiracies that are propagated around this story," Earnest said.
"The fact of the matter is, 67,000 e-mails either sent by or received by Lois Lerner have been provided to Congress. So if we are trying to hide Lois Lerner's e-mails from congressional oversight, there's a pretty large loophole. Thousands of those e-mails actually relate to the time period covered by the hard drive crash that you referred to."
Earnest said the IRS has been working to track down emails Lerner sent between January 2009 and April 2011 -- the most critical timeframe, congressional investigators say.
The IRS has produced "tens of thousands" of Lerner's emails, Earnest said, apparently by checking the email files of other IRS employees who corresponded with her.
"So there is ample evidence to indicate that a good-faith effort has been made by the IRS to cooperate with congressional oversight. And the far-fetched skepticism expressed by some Republican members of Congress I think is not at all surprising and not particularly believable."
Lerner formerly headed the IRS division that processes requests for tax-exemption. Conservative tea party groups complained that their applications were singled out for inappropriate scrutiny and delay before the 2010 midterm election.
Three congressional committees are investigating Lerner's role in the scandal, and the vanished emails might have indicated whether people outside the IRS were also involved in efforts to suppress conservative groups.
Rep. Dave Camp (R-Mich.), chairman of the House Ways and Means Committee, said it's "completely unacceptable" that he is just learning about the vanished emails more than a year into his committee's investigation of the Lerner/IRS scandal.
"Due to a supposed computer crash, the agency only has Lerner emails to and from other IRS employees during this time frame. The IRS claims it cannot produce emails written only to or from Lerner and outside agencies or groups, such as the White House, Treasury, Department of Justice, FEC, or Democrat offices," Camp wrote in a message posted on his website.
He said the email situation "calls into question the credibility of the IRS’s response to Congressional inquiries.
"There needs to be an immediate investigation and forensic audit by Department of Justice as well as the Inspector General," Camp said.