Washington (CNN) The top lawyer at the FBI when the Russia investigation was started said Friday that the probe was opened for "lawful, legitimate reasons," and pushed back on conspiracies that President Donald Trump has spread about the origins of the investigation.

James Baker, the former FBI lawyer, said he felt compelled to speak out amid growing scrutiny of how the investigation started, concerns that have been stoked by Trump and Attorney General William Barr, who is conducting an internal review to see if there was any misconduct.

Almost all of the top FBI officials who oversaw the Russia investigation have now publicly spoken out against Trump, an extraordinary and unprecedented rebuke of a sitting president.

"There was a point in time relatively recently where I just became sick of all the BS that is said about the origins of the (Russia) investigation, and I just got fed up with it," Baker said.

"I want to talk about the origin of the investigation to reassure the American people that it was done for lawful, legitimate reasons and was apolitical throughout, in my experience."

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