Fox News legal analyst Andrew Napolitano told The Daily Caller that, during its investigation of former CIA Director David Petraeus and his biographer, the FBI appears to have wrongfully treated a simple domestic dispute like a national security or criminal matter.

“David Petraeus didn’t betray his country,” Napolitano said in a phone interview. “He betrayed his wife. Big deal.”

Napolitano said the federal investigation was “the use of law enforcement either for a personal vendetta that [Tampa military liaison Jill] Kelley pushed through her FBI agent connection, or a political vendetta — somebody wanting to silence, by embarrassing, humiliating and destroying the credibility of Petraeus.”

“Not only does it not appear there was a crime committed,” Napolitano continued, “[and] not only does it not appear that there was a national security implication, but this is hardly the type of thing that the FBI investigates. This was instigated, apparently, by the Kelley woman, and her friend in the FBI. That is an inappropriate means to commence an investigation by the FBI.”

Napolitano, who is a former New Jersey Superior Court judge, said federal agents, like members of the judiciary, are typically prohibited from working on cases that present a conflict of interest. (RELATED: CIA denies claim it held hostages at Libya annex)

“In fact, the FBI has an internal rule that if an FBI agent knows the complainant, the victim or the target, that FBI agent cannot have anything to do with the case, because that often clouds an individual’s judgment,” Napolitano continued. “It’s like a judge trying a case in which he knows one of the parties. It’s prohibited, and the judge has to reveal that, and get off the case. The principle is the same for the FBI. For that reason, I don’t believe the government’s version of these events.”

According to numerous reports, the FBI began its investigation after Kelley told an agent, whom she knew as a friend, that she had received harassing emails from an anonymous source. The emails, which the agency eventually traced back to Petraeus biographer Paula Broadwell, appeared to be an attempt to intimidate Kelley into staying away from Petraeus.

“It’s inconceivable that the FBI decided to do an investigation based on one email between two private people, whether it mentions Petraeus’ name or not,” Napolitano added. “I don’t know what criminal charges could be filed. It’s not a crime for Mrs. Broadwell to send an email to Mrs. Kelley saying, ‘Stay away from my guy.’”

The FBI agent Kelley contacted with her initial complaint apparently became personally invested in the investigation, and sent shirtless photographs of himself to Kelley, according to numerous reports. A lawyer for the agent, who has been identified as FBI veteran Frederick Humphries, admitted this week that the pictures were sent “years ago” as part of a “larger context of what I would call social relations in which the families would exchange numerous photos of each other.”

Somehow, the FBI obtained personal emails between the different parties involved, including Kelley, Broadwell, Petraeus and others. Unless those individuals voluntarily surrendered their emails — a possibility that, while it appears unlikely, has not been ruled out — Napolitano said there are only a few equally troubling ways by which the FBI could have obtained the emails.

“In order for the FBI to read your emails, my emails, Tucker Carlson’s emails – they need a search warrant,” Napolitano told TheDC. “They can only get a search warrant in one of two ways under the current law: They could go to a federal judge and demonstrate probable cause of crime – meaning that [they have evidence] Petraeus probably committed a crime, or in my hypothetical [they have evidence] Tucker Carlson, you or me [committed a crime]. That’s hardly the case here. Or, under the [USA] Patriot Act, they could write their own search warrant if they satisfy themselves – a dubious and unconstitutional standard, but that’s the law no less: if they satisfy themselves that terrorist activity was afoot, [which is] also an irrelevant and absurd consideration here. So that means I don’t how they could have gotten a search warrant.”

“The third way they could have gotten his emails is without a search warrant by hacking into the CIA’s computers, in which case they [would have] violated criminal law themselves,” Napolitano added. “They’ve done it before – they’re probably doing it as we speak – but this would be a public violation of criminal law by the agents that did [if that’s the case].”

Napolitano said he suspects the reason the FBI, Justice Department and White House may have undertaken these actions against Petraeus is that he “obviously knew what happened in Benghazi.” (RELATED AUDIO: Limbaugh says media will ‘destroy’ Petraeus if he gives new details on Benghazi)

“Either it was an ‘innocent flash mob,’ as he told the Senate and House intelligence committees on Sept. 14, an organized terrorist attack, as most of us believe, or something far more sinister, like that it was a CIA detention center, and people were being tortured there – that would violate federal law, it would violate the president’s public statements and would violate the president’s executive order prohibiting such activity,” Napolitano said.

“They probably don’t plan any prosecutions,” he added. “This is being leaked by people who want to destroy Petraeus, and the leaks are a violation — not of federal criminal law, because there is no criminal investigation — the leaks are a violation of FBI regulations and Justice Department regulations. The leaks are enough to get FBI agents fired – or whoever is doing the leaking, but not to get them prosecuted. The only way the leaker could be prosecuted is if this information was part of an ongoing criminal investigation to be presented before a grand jury. If that is leaked, that violated federal criminal law.”

Since no criminal charges have been filed, and since none are expected to be filed, the information the FBI obtained should legally never have been allowed to see the light of day.

“Whoever is doing the leaking wants to smear Petraeus, because they don’t want him to confront the mountain of evidence that exists which would contradict the testimony he gave on Sept. 14,” Napolitano said. “Sept. 14 is three days after Benghazi and two days before [U.N. Ambassador] Susan Rice’s infamous interviews. Petraeus probably said what the political hacks in the White House told him to say. Sept. 14 is also the height of the presidential campaign. So, the world is very different now.” (RELATED VIDEO: Obama’s defense of Susan Rice on Wednesday was his ‘usual show’ of indignation, Krauthammer says)

“The entity that wants to affect the outcome here [in the Benghazi scandal], the White House, does not want Petraeus confronted with the mountain of evidence that would contradict what he said on Sept. 14,” Napolitano added. “So, the only way they can prevent that confrontation is to destroy him.”

That alleged plan didn’t fully work, though. Petraeus has since agreed to testify before congressional intelligence committees about the scandal.

On Wednesday morning, the Senate intelligence committee chairwoman, California Democratic Sen. Dianne Feinstein, announced Petraeus’ decision to come forward and testify before her committee on Benghazi. “Mr. Petraeus has indicated his willingness [to testify],” Feinstein said. “He is eager to come before the committee so we will work out the details.”

Feinstein said she was as shocked as anybody when news of the Petraeus scandal broke, because the law enforcement authorities conducting the investigation failed to inform congressional intelligence committee leaders about what was going on. She said the news felt like getting struck by a “lightning bolt.”

Napolitano said that, “in one respect,” he’s “almost glad” that intelligence officials in Congress were kept in the dark. That’s because he thinks the decision to surprise congressional leaders with this news “will cause the less partisan and more intellectually honest Democrats – there are only a few of them, but Feinstein is one of them – that will cause them to grab the president by the lapel saying, ‘What the hell is going on here?’ So, in that respect, we can enjoy the fruits of divided government, because the Republicans in the House won’t let this go, and intellectually honest Democrats like Dianne Feinstein won’t let this go.”

Ultimately, though, Napolitano said he doesn’t think FBI, Justice Department and White House officials could have told Congress about the scandal ahead of time, because leaders of both parties in Congress would have seen it as a political agenda-driven stunt, instead of a legitimate investigation.

“Those people would have seen right through it,” Napolitano said. (RELATED: Obama reportedly signs secret order giving military more cybersecurity teeth)

Napolitano also warned that all Americans should be worried that the federal government could be reading their emails, too – and this is a “wake-up call.”

“This has been going on since the Patriot Act,” he said. “The Patriot Act lets federal agents write their own search warrants on the flimsiest of grounds, with no judicial review. This has been used – and these are Justice Department figures, so you can assume it’s been used more than the Justice Department tells us – over 250,000 times.”

“Now, this is only reviewed by a judge when evidence obtained from one of these search warrants is used in a criminal prosecution. Otherwise, there’s no judge involved. The FBI hacks into an email account, gets what it wants, the person whose email account is hacked doesn’t even know it, unless the government is going to prosecute them, and that prosecution used what the FBI got. Only then does a judge review what the FBI did. So, this is bringing us several steps closer to a police state, because if they can do this to David Petraeus, they can do this to anybody.”

Moving forward, Napolitano said he expects congressional investigators to clamp down in an effort to uncover what really happened. But he warned that the focus should be on figures like FBI Director Robert Mueller, not those already exposed as political operatives, like Attorney General Eric Holder.

“I would not dwell on Holder, because he’s a political hack,” he said. “I would dwell on Mueller, who’s the head of the FBI and who’s not a political hack, who’s a serious guy. Mueller enjoys the reputation today that Petraeus had two weeks ago. Mueller meets with the president every week without the attorney general there. It is inconceivable that he knew – his agents were reading the emails of the director of the CIA and the director’s mistress – and did not tell the president. So, either the FBI agents didn’t tell him [Mueller], in which case they broke the law, or he didn’t tell the president, in which case he should be fired for not telling the president about something of this magnitude. I think he knew, I think he told the president and the president just kept it under wraps until after Election Day, so that what we now see unfolding did not happen before Election Day and tear his political fortunes.”

Follow Matthew on Twitter