House investigators probing the IRS’s targeting of Tea Party groups have learned that Lois Lerner, the official who oversaw that program, used her private email account for government business, prompting House Republicans to wonder if Lerner used the email account to avoid congressional review.

“[A]dditional documents related to the Committee’s investigation may exist in these non-official accounts over which you have some control, and the lack of access to this information prevents the Committee from fully assessing your actions,” House Oversight and Government Reform Committee chairman Darrell Issa, R-Calif., wrote to Lerner in a letter Tuesday after learning that she forwarded some IRS documents to a personal MSN email account labeled “Lois Home.”

Lerner headed up the tax exempt division that submitted 292 Tea Party groups to extra scrutiny, compared to just 6 progressive groups, according to a Treasury Department inspector general.

Issa called Lerner to testify in a House hearing on the targeting, but she refused to testify, citing her 5th amendment rights.

“They can obtain her testimony tomorrow by doing it the easy way … immunity,” William W. Taylor III, Lerner’s lawyer, told Politico after the hearing. “That’s the way to resolve all of this.”