Why didn’t Congress know earlier that the Internal Revenue Service had targeted conservative groups for special scrutiny? In days of hearings, lawmakers have tried to get a satisfactory answer from witnesses under oath. They haven’t succeeded.

According to a Treasury Department inspector general’s report, Lois Lerner, a mid-level IRS manager, learned in 2011 that her division had flagged applications for tax-exempt status that had come from organizations with “tea party” and similar terms in their titles. She told her employees to stop, which they did, but then they resumed some months later. When members of Congress later asked questions about the scrutiny some conservative groups were getting, why didn’t she reveal this history?

Lawmakers say that Lerner, who was placed on administrative leave Thursday, had plenty of opportunity. Leaders of the House Oversight and Government Reform Committee, for example, claim that in a May 4, 2012, letter to them, she defended the questioning of tea-party applicants whom the agency had singled out. Yet, they also point out, we now know that, in an internal review that very month, the IRS deemed seven demands it had made of applicants as irrelevant or unnecessary.

The inspector general, meanwhile, reports that by April 25, 2012, Lerner’s senior technical adviser already had found a list of questions the IRS has been asking to be inappropriate. On Wednesday, Lerner insisted she hadn’t done anything wrong, then refused to testify, citing her Fifth Amendment right against self-incrimination.

Others also failed to be forthright. Following media attention and questions from Congress, then-Deputy Commissioner Steven T. Miller apparently ordered his own review in March 2012, and he got the results that May. Why did it take a year — and the intervention of the inspector general — for the agency to reveal the targeting? In testimony before House lawmakers, Miller said that he had “answered questions as they were asked” — and they were asked before he found out what was going on.

In a session before a Senate panel, Douglas Shulman, who headed the IRS when the targeting happened, said that he didn’t volunteer more information because he wanted to wait for the inspector general to complete his work. Does that mean he would have stayed silent if the inspector general hadn’t forced the matter?

Even if Lerner, Miller and Shulman didn’t know a thing about the agency’s targeting when lawmakers asked each of them about it — a problem in itself — they all should have informed Congress when they did find out. By not doing so, they misled lawmakers, and they demonstrated a lack of seriousness about the breach of trust for which the IRS is responsible.

With leadership like that, it should be little wonder that the misbehavior didn’t end in 2011, when Lerner first ordered it to stop, but restarted and festered until last year.

It is too bad that worries about criminal liability have now begun to hamper lawmakers’ questioning. If investigators have to offer players such as Lerner immunity, fine. Locking people up is less important than figuring out exactly what happened — and making sure it never occurs again.

Editorial by The Washington Post