The inspector general’s follow-up report on the so-called “exigent” letters — an investigation that started in 2007 — is due in a few months. E-mails obtained by the Post showed that responsible agency officials informed superiors in 2005, but the practice continued for two more years.

While it looks as if the nation’s top law enforcement agency routinely violated the nation’s wiretapping laws for years, it seems no one will actually be prosecuted since the violations are being judged as merely “technical.”

Agents in the Federal Bureau of Investigation’s terrorism investigation unit in New York City began using so-called “exigent letters” shortly after 9/11 as a shortcut around a proper terrorism subpoena, known as a National Security Letter. A proper NSL authorized under the Patriot Act allows agents to secretly get an individuals’ phone and financial records with a self-issued subpoena so long as they are “relevant” to an official, ongoing investigation.

That was supposed to prevent FBI agents from getting someone’s phone number just for exercising their First Amendment rights. But the standard was low enough that agents began issuing tens of thousands of NSLs a year, with not one being checked by a judge.

But even those rules were too stringent, and the New York-style “exigent letter” — an understandable shortcut after the 9/11 attacks — graduated from being temporary and was adopted by employees in Washington, D.C.

The news comes as Congress contemplates tightening the safeguards around NSLs following what has become an ever-growing list of abuses of FBI powers.

Even though supervisors and legal counsel became of aware of the fake emergency letters in 2004, the illegal behavior continued. But the phone companies began pushing back against the requests because they were being left with the legal liability. The public became aware of the NSL abuse in 2007, when the Justice Department’s inspector general released a report on the use of the power.

Documents show that senior FBI managers up to the assistant director level approved the procedures for emergency requests of phone records and that headquarters officials often made the requests, which persisted for two years after bureau lawyers raised concerns and an FBI official began pressing for changes.

“We have to make sure we are not taking advantage of this system, and that we are following the letter of the law without jeopardizing national security,” FBI lawyer Patrice Kopistansky wrote in one of a series of early 2005 e-mails asking superiors to address the problem.

The FBI acknowledged in 2007 that one unit in the agency had improperly gathered some phone records, and a Justice Department audit at the time cited 22 inappropriate requests to phone companies for searches and hundreds of questionable requests. But the latest revelations show that the improper requests were much more numerous under the procedures approved by the top level of the FBI.

In fact, the real number is 2,200 illegal requests out of a total of 4,400 so-called exigent requests, the Post reports.

When FBI personnel attempted to provide NSLs to cover the requests after the fact, they often couldn’t because the requests came from higher-up personnel and there was often no open-case to tie the request to. Department guidelines require NSLs to be tied to specific cases. Agents finally created blanket NSLs that covered multiple requests — one NSL was for threats to aviation, another was for threats to individuals.

Then the FBI decided just to issue on NSL to cover all that was left, the Post reports.

“What is new in the Post’s reporting today is that it was FBI supervisors and senior officials who were abusing the system,” said Greg Nojeim, a lawyer at the Center for Democracy and Technology.

“The FBI has been assuring us for years that the abuses of the Patriot Act could be cured by more layers of internal review, but now we learn that the supervisors themselves were abusing the process,” Nojeim said. “When people are under pressure, internal review is not enough, there needs to be external oversight, and the best way to do that is to have a judge look at the situation.”