The special counsel Robert Mueller has interviewed Dana Boente, the FBI general counsel.

Former FBI director James Comey called Boente right after he received a phone call from President Trump last year during which Comey said Trump asked him to "lift the cloud" of the Russia investigation.

Mueller is in possession of contemporaneous notes Boente took documenting his conversation with Comey about the phone call with Trump, and they appear to corroborate critical portions of Comey's congressional testimony last year.

The special counsel Robert Mueller has interviewed FBI general counsel Dana Boente to interview with his team as part of the Russia investigation, The Washington Post reported.

Mueller is tasked with probing Russia's interference in the 2016 US election and whether President Donald Trump's campaign colluded with Moscow to tilt the race in his favor. He is also looking into whether Trump sought to obstruct justice when he fired FBI director James Comey last May.

Boente revealed Mueller had asked to interview him in a letter to the Justice Department's senior most career attorney, Scott Schools, on January 2, according to MSNBC.

At the time, Boente was the acting head of the national security division at the DOJ. Boente said in the letter that he did not believe he was a subject or target of the investigation.

Boente may prove to be a pivotal witness in Mueller's obstruction case against Trump. The case hinges, in large part, on determining Trump's rationale behind firing Comey.

The White House initially said Comey was fired because of how he handled the bureau's investigation into former Secretary of State Hillary Clinton's use of a private email server to conduct government business. But Trump later said on national television that "this Russia thing" was a factor in his decision. He also reportedly told two top Russian government officials the day after Comey was ousted that his firing had taken "great pressure" off of him.

Comey testified to the Senate Intelligence Committee last year that Trump had repeatedly broached the topic of the Russia investigation in private meetings and phone calls when he was FBI director. Comey told the panel he documented the conversations in contemporaneous memos and informed senior DOJ officials of them as well.

Boente was one of those officials. And according to handwritten contemporaneous notes MSNBC's Rachel Maddow obtained this week, he can corroborate critical parts of Comey's testimony to Congress, which the White House cast as false and misleading. Mueller is in possession of the notes.

Boente was not with Comey during any of the alleged meetings or calls. Instead, his significance as a witness stems from his memo documenting a March 30, 2017 phone call during which Comey told him the president had called him earlier and complained about the Russia investigation.

Notes taken by law enforcement and government officials are known as MFRs, or memoranda for the record. It is common for officials to maintain notes of sensitive meetings. The contemporaneous memos created by FBI agents, in particular, are widely viewed as credible evidence in courts.

Boente's notes documenting his conversation with Comey line up with key portions of Comey's congressional testimony, both written and spoken.

Comey said in his written testimony that during the March 30 call, Trump "described the Russia investigation as a cloud that was impairing his ability" to carry out his job, and subsequently asked if Comey could "lift the cloud."

The former FBI director later told Sen. Dianne Feinstein, the ranking member on the Senate Intelligence Committee, that he interpreted the statement to mean that Trump was "frustrated" the Russia probe "was taking up so much time and energy ... and it was making it difficult for him to focus on other priorities of his."

The top line of Boente's memo documenting his call with Comey that March says: "Comey. March 30, 2017. 8:13AM."

After the phone call, in which Comey told Congress he recounted his conversation with the president that had concluded just minutes earlier, Boente wrote: "Cloud as a result of Russia [business]. This makes running the country difficult."

According to the notes, Comey then recounted Trump's request, saying, "What can I do to relieve the cloud..."

In his written testimony, Comey said that after Trump asked what he could do to "lift the cloud," he responded that the FBI was investigating the matter "as quickly as we could, and that there would be a great benefit, if we didn't find anything, to our having done the work well."

"The President agreed, but then re-emphasized the problems this was causing him," Comey said.

Former FBI Director James Comey testifies on Capitol Hill. Drew Angerer/Getty Images

Boente's memo said: "Kept coming back to it making it hard to do business for the country..."

"We will do the work well," the memo continued.

Comey also told Congress that he had told the president that he was not personally under investigation at the time. He added that Trump had asked him to "get out" that he was not under investigation.

Boente's notes said: "Reminded him we are not investigating you. That would be great to get out."

Later, Comey told lawmakers that he had raised concerns to Attorney General Jeff Sessions about Trump's behavior, telling Sessions that "it can't happen that you get kicked out of the room and the president talks to me."

Boente's notes recounted, "Told AG — before recusal — I cannot be speaking with the President alone."

Comey said as much in his upcoming book, "A Higher Loyalty: Truth, Lies, and Leadership."

According to an excerpt from the memoir published by The Washington Post, Comey wrote that when Trump asked him in February 2017 to let go of the bureau's investigation into former national security adviser Michael Flynn, Comey regretted not interrupting Trump to tell him he was wrong to make the request.

When Comey later confronted Sessions about his conversations with Trump, Sessions was "both overwhelmed and overmatched by the job," Comey wrote.

"Sessions just cast his eyes down at the table, and they darted quickly back and forth, side to side," Comey added. "He said nothing. I read in his posture and face a message that he would not be able to help me."

Boente's notes will likely contribute significantly to bolstering Comey's version of events surrounding his conversations with Trump.

The president, meanwhile, has repeatedly called the Russia investigation a "witch hunt" and a "hoax." His lawyers had been in talks with Mueller about setting up a potential interview with Trump regarding the obstruction case, but they unraveled after Trump grew enraged following reports that the FBI had raided the home and office of his personal lawyer, Michael Cohen.

After learning of the raids, Trump decided not to grant Mueller an interview. Regardless, Mueller will reportedly move ahead with compiling a report of his findings in the case without an interview, and legal experts said he likely has enough evidence to wrap up the investigation even without a sit-down with the president.

According to NBC News, Mueller's findings could come out as early as May and as late as July.