Photos: Key players in the IRS scandal

IRS Commissioner John Koskinen is facing tough questions about an unknown number of missing agency e-mails due to hard drive crashes. Republicans are especially interested in e-mails belonging to former IRS official Lois Lerner as lawmakers investigate the agency's targeting of conservative tax-exempt groups.

IRS Commissioner John Koskinen is facing tough questions about an unknown number of missing agency e-mails due to hard drive crashes. Republicans are especially interested in e-mails belonging to former IRS official Lois Lerner as lawmakers investigate the agency's targeting of conservative tax-exempt groups.