James Comey. Kevin Lamarque/Reuters FBI Director James Comey explained Wednesday why he commented in late October on reopening the investigation into Democratic presidential nominee Hillary Clinton's use of a private email server but not on the bureau's ongoing investigation into whether President Donald Trump's associates colluded with Russia.

Comey said the reason was that he had testified under oath that the Clinton investigation was wrapped up but had never commented publicly on the FBI's investigation into Trump and Russia.

During the Senate Judiciary Committee hearing Comey was testifying at, Democratic Sen. Patrick Leahy of Vermont asked about the discrepancy.

"You sent a letter informing the Senate and House that you were reviewing additional emails that could be relevant," Leahy said. "Both investigations were open, but you still only commented on one."

Comey defended his decision.

"I commented, as I explained earlier, on October 28 in a letter that I sent to the chair and ranking [members] of the oversight committees that we were taking additional steps in the Clinton email investigation because I had testified under oath repeatedly that we were done — that we were finished there," Comey said.

"With respect to the Russia investigation, we treated it like we did with the Clinton investigation. We didn't say a word about it until months into it, and then the only thing we've confirmed so far about this is — the same thing as with the Clinton investigation — that we are investigating.

"And I would expect that we're not going to say another peep about it until we're done. And I don't know what will be said when we're done, but that's how we handled the Clinton investigation as well."

Comey sent a letter to congressional leaders in late October — 11 days before the November election — saying the FBI was reviewing emails tied to Clinton's use of a private server while she was secretary of state that were found as a part of a separate investigation into disgraced New York City politician Anthony Weiner.

The letter, which implied a reopening of the Clinton investigation, reverberated through the Clinton and Trump campaigns.

Comey announced days later that nothing was found in the additional emails.

Then in March, Comey said during a House Intelligence Committee hearing that the FBI was investigating whether the Trump campaign colluded with Russian officials to help swing the election in Trump's favor. He said the investigation launched in late July.

Leahy said that during his four decades as a US senator, he couldn't remember seeing anything like the FBI's actions with the Clinton investigation.

"Was it appropriate for you to comment on one investigation repeatedly and not say anything about the other?" Leahy said.

"I think so," Comey said.

"I think I treated both investigations consistently under the same principles," he added. "People forget, we would not confirm the existence of the Hillary Clinton email investigation until three months after it began, even though it began with a public referral and the candidate herself talked about it. In October of 2015, we confirmed it existed."