O'Connor said that then acting IRS Commissioner Dan Werfel was emphatic in directing that the agency turn over documents as fully and quickly as possible in response to congressional requests.

But when she arrived, O'Connor saw an IRS that did not have the resources in place for such an operation.

"We (needed) to add people because the IRS had never encountered anything like this," O'Connor told the panel. "We didn't have the staff in place to do this kind of document review production."

She added that the agency also had to add significant server capacity to handle the requests.

"I think the record of the IRS reflects very very hard work to produce the documents," O'Connor concluded.