We're starting to understand why Lois Lerner took the Fifth about her role in the IRS targeting of conservative groups. The testimony of at least three more employees in the IRS Washington office is now making clear that Ms. Lerner and other Washington IRS officials had a direct hand in slow rolling the tax-exempt applications of conservative groups in an election season.

The House Oversight Committee holds another hearing Thursday that will showcase some of these witnesses. According to Washington IRS tax law specialist Carter Hull, his supervisor Ronald Shoemaker and Manager of Exempt Organizations Technical Michael Seto, tea party applications were intentionally singled out for extra layers of review and put through an unusual process.

Mr. Hull told House investigators that normally his judgment about applications would have been enough to approve or deny their tax-exempt status. Instead of sending those applications through the normal channel, however, conservative applications were sent through Ms. Lerner's office for review, and also directed to the IRS chief counsel. That process was highly unusual and created a vetting system in which applications were interminably delayed.

According to Mr. Hull, starting in April 2010, he was told by a supervisor to give extra attention to some tea party applications as a trial run for how the agency might handle such cases going forward. As part of that process, he was instructed to send the applications through Ms. Lerner's office and the office of IRS Chief Counsel William Wilkins for additional scrutiny.

Once he delivered them, however, the process stalled and the applications mouldered until August 2011, when Mr. Hull met with Mr. Wilkins's staff and Ms. Lerner's senior adviser to discuss the applications. Mr. Hull was told the applications had been on the shelf too long and needed updating. "I was taken aback," Mr. Hull said of the request, which added even more time to the already delayed applications. "I hadn't had the case for a while. I couldn't ask if I didn't have the case."