On Sept. 2, the FBI released a lengthy explanation of its investigation of Hillary Clinton and a summary of the evidence amassed against her. It also released a summary of Clinton's July FBI interrogation.

The interrogation was in some respects standard and in others very troubling. It was standard in that she was confronted with emails she had sent or received and was asked whether she recalled them, and her judgment about them was challenged. The FBI was looking for gross negligence in her behavior about securing state secrets.

The failure to secure state secrets that have been entrusted to one for safekeeping is known as espionage, and espionage is the rare federal crime that does not require prosecutors to prove the defendant's intent. They need only prove the defendant's gross negligence.

At one point during the interrogation, FBI agents attempted to trick her, as the law permits them to do. Before the interrogation began, agents took the hard copy of an innocuous email Clinton had sent to an aide and marked it "secret." Then, at her interrogation, they asked Clinton whether she recognized the email and its contents. She said she did not recognize it, but she questioned the "secret" denomination and pointed out to the agents that nothing remotely secret was in the email.

In this dangerous world, how can a person seeking the presidency be so dumb or ignorant or indifferent or reckless or deceptive about what is a secret and what is not?

By examining the contents of the email to see whether it contained state secrets, which it clearly did not, Clinton demonstrated an awareness of the law -- namely, that it is the contents of a document or email that cause it to be protected by federal secrecy statutes, not the denomination put on it by the sender.

This added to the case against her because she later told the FBI that she had never paid attention to whether a document contained state secrets or not. In the strange world of espionage prosecution, this denial of intent is an admission of guilt, as it is profoundly the job of the secretary of state to recognize state secrets and to keep them in their secure government-protected venues, and the grossly negligent failure to do so is criminal.

The FBI notes of the interrogation recount that Clinton professed serious memory lapses 39 times. She also professed ignorance over what "C" means in the margin of a government document. "C" in the margin means "confidential," which is one of the three levels of federal state secrets. The other two levels are "secret" and "top secret." Under federal law, Clinton was required to keep in secure government venues all documents in those three categories. The FBI found that she had failed to do so hundreds of times.

By denying that she had paid attention to notes in margins designating the presence of secrets, by denying that she recognized a secret when she saw one and by denying that the location of planned drone strikes is secret (an obvious secret with which FBI agents confronted her), she succeeded in avoiding incriminating herself.

But by saving herself from indictment, she may have doomed her campaign for president. In this dangerous world, how can a person seeking the presidency be so dumb or ignorant or indifferent or reckless or deceptive about what is a secret and what is not?

The records released last week also reveal that the FBI must have been restrained from the outset from conducting an aggressive investigation. It did not present any evidence to a grand jury. It did not ask a grand jury for any subpoenas, and hence it didn't serve any. It did not ask a judge for any search warrants, and hence it didn't serve any. The data and hardware it gathered in the case were given to it in response to simple requests it made.

I counted five times in the report where the FBI lamented that it did not have what it needed. This is the FBI's own fault. This tepid FBI behavior is novel in modern federal law enforcement. It is inimical to public safety and the rule of law. It is close to misconduct in office by high-ranking FBI officials.

Someone restrained the FBI.

The FBI did not ask Clinton aggressive follow-up questions. Her interrogators just blithely accepted her answers. They failed to present her with documents she had signed that would have contradicted what she was telling them -- particularly, an oath she signed on her first day in office promising to recognize state secrets when she came upon them and to keep them in secure venues. And agents violated Department of Justice policy by not recording her interrogation when her lawyers told them she would not answer questions if her answers were recorded.

Now the FBI has interjected itself into the presidential campaign by releasing these documents. Notwithstanding the mountain of evidence pointing to Clinton's guilt, it is highly improper and grossly unfair to release evidence gathered against a person who will not be prosecuted. Moreover, it is tendentious to release only part of the evidence -- only what agents want the public to see -- rather than the complete file. Yet all this evidence is secret under DOJ regulations. Had any of it been intended for or presented to a grand jury, the release of it would have been criminal.   

What happened here? The FBI seriously dropped the ball, and Clinton was more concerned about being indicted than she was about losing the race for the presidency.          

It is apparent that some in FBI management blindly followed what they were told to do -- exonerate Hillary Clinton. There is no other explanation for the FBI's failure from the outset to use ordinary law enforcement tools available to it. Yet some in the FBI are not professionally satisfied by this outcome. They know that a strong case for prosecution and for guilt is being ignored for political reasons.

What else do they know?

Andrew P. Napolitano, a former judge of the Superior Court of New Jersey, is the senior judicial analyst at Fox News Channel.