"Bill Barr on CBS offers no facts. An AG should not be echoing conspiracy theories. He should gather facts and show them. That is what Justice is about," Comey, the onetime FBI director, tweeted on Saturday.
While it's unclear exactly which comments Comey was referring to, Barr reportedly told CBS that the Justice Department had made a mistake in the way it carried out the Russia investigation.
"I think the activities were undertaken by a small group at the top which is one of the ... probably one of the mistakes that has been made instead of running this as a normal bureau investigation or counterintelligence investigation. It was done by the executives at the senior level, out of headquarters," he said.
This wasn't the first time Comey attacked Barr. In May, he called out the attorney general for "sliming his own department."
Comey has vehemently defended his former agency, arguing in an op-ed Tuesday that investigators did the best they did with the information they had.
"There was no corruption. There was no treason. There was no attempted coup. Those are lies, and dumb lies at that. There were just good people trying to figure out what was true, under unprecedented circumstances," he said before attacking the way President Trump has portrayed the Russia investigation.
Trump, who has frequently called the investigation a "witch hunt," authorized Barr to declassify information from the intelligence community in order to facilitate a deep-dive look at the Russia probe's origins.