U.S. Rep. Erik Paulsen and House Republicans hammered the commissioner of the Internal Revenue Service on Friday over missing emails related to its targeting of conservative groups.

The IRS announced last week that it can't find two years of emails from Lois Lerner, the former head of the IRS division that oversaw tax-exempt groups. Lerner has acknowledged the agency's singling out of Tea Party groups that sought tax-exempt status from February 2010 through the 2012 election.

While testifying before the House Ways and Means Committee, Commissioner John Koskinen blamed the lost emails on an antiquated email system and a computer crash. Paulsen and other GOPers maintain the missing messages are part of a massive cover-up.

"Can you rule out that Lois Lerner destroyed her own computer?" Paulsen asked.

In response, Koskinen said: "There's no evidence that she did. You can never rule out something that you don't know."

In a statement following the hearing, Paulsen said: "It's long past time for the IRS to stop misleading Congress and the American people. The IRS systematically targeted individuals based on their personal beliefs, and as we found out today, is continuing to cover up their misdeeds."

Michigan Rep. Sandy Levin, the lead Democrat on the House Ways and Means Committee, said there was no conspiracy behind the computer crash, just an email system that was underfunded and deficient.