The IRS erased computer backup tapes likely containing Lois Lerner's emails even though they were told to preserve the evidence just months before, the lead investigator for the IRS revealed Thursday.

Shortly after officials discovered that emails relating to the IRS tea party scandal had been lost, IRS employees erased as many as 24,000 emails on 422 backup tapes, J. Russell George, the Treasury inspector general for tax administration, told the House Oversight and Government Reform Committee on Thursday, reported The Washington Times.

The tapes "most likely" contained Lerner's emails, George said.

George said that employees magnetically degaussed the tapes around March 4, 2014, by accident rather than in an attempt to destroy evidence. Nevertheless, he said that the destruction still defied a preservation order, reports Fox News.

"We have been misled. They destroyed evidence. That's what they did," said House Oversight Committee Chairman Jason Chaffetz, R-Utah, according to the Times.

Chaffetz continued: "It just defies any sense of logic. It gets to the point where it truly gets to be unbelievable. Somebody has to be held accountable," reports The Associated Press.

Deputy Inspector General Timothy Camus laid the blame on two "lower-graded" employees at the IRS center in Martinsburg, West Virginia. He said the employees did not completely understand the IRS directive to not destroy backup tapes.

"When interviewed, those employees said, 'Our job is to put these pieces of plastic into that machine and magnetically obliterate them. We had no idea that there was any type of preservation (order) from the chief technology officer,' " Camus told the committee, AP reports.

Rep. Thomas Massie, R-Ky., asked Camus if the employees erased the tapes due to incompetence, to which Camus responded, "One could come to that conclusion."

George released a report in 2013 detailing how IRS agents had improperly and purposefully singled out conservative groups for additional scrutiny when they applied for tax-exempt status. Agents had guidance to watch for an "emerging issue" of conservative groups applying for tax exempt status, and flagged the groups as potentially "political."

As a result, nearly 300 conservative groups had their applications delayed for years and some were asked "unnecessary, burdensome questions" about past and future donors and activities. Nine tea party groups were still awaiting IRS approval as of the beginning of May, according to The Washington Times.

Lerner headed the application processing division at the time, and was forced to resign along with other top leadership following the release of George's report.

Congressional investigators were able to prove that IRS officials in Washington knew that conservative groups were being targeted, and were hoping that Lerner's lost emails would help their investigation, according to AP.