It was "absolutely unfair and unethical" for FBI Director James Comey to give a "progress report" on the investigation into Hillary Clinton's email server by sending a letter to congressional leaders alerting them of the discovery of further potential evidence, and not fair to the Democratic presidential nominee, retired judge and Fox News contributor Anthony Napolitano said Monday.

"How unfair to Mrs. Clinton," Napolitano, the guest on Fox News' "Outnumbered" program commented. "She has constitutional rights like the rest of us."

With his letter, Napolitano said, Comey was announcing "'we have something on you. We can't tell you what it is.'"

Napolitano said it is "odd" to be on the same page as former Attorney General Eric Holder, who wrote in an opinion piece for The Washington Post that Comey's decision was "incorrect" and "violated longstanding Justice Department policies and tradition."

"It is absolutely unlawful and unethical for anybody in law enforcement to give a progress report on an investigation midstream," Napolitano said. "He should not have sent the letter . . . he should have have unleashed the FBI agents to do all digging [they] can."

If the agents could find evidence, the retired judge continued, then Comey would send that to the Justice Department, which would decide if it should head to a grand jury for a potential indictment, not be revealed "midstream."

Meanwhile, the FBI did not obtain a search warrant to investigate the emails, which were discovered on a laptop owned by former Congressman Anthony Weiner and used by his now-estranged wife, close Clinton aide and confidant Huma Abedin, until Sunday night.

"The application to induce the judge to sign the search warrant did not mention Hillary Clinton," said Napolitano, and investigators are looking into allegations Weiner was sexting with an underage girl.

As far as Abedin is concerned, "what is the criminal basis? That Huma did not tell the truth when she was interrogated by the FBI because they now have evidence that contradicts it?" Napolitano said. "Do we have all of your emails they asked her in the interrogation? Yes, you do. Then they find 650,000 emails she didn't tell them about."

Napolitano also disagreed with Senate Minority Leader Harry Reid's contention Comey is in violation of the Hatch Act, which prohibits federal authorities from becoming involved in elections.

"That prohibits them from using federal assets, federal time or the aura of their office to campaign, not to make a law enforcement decision that has an effect on a campaign," Napolitano said.