Former FBI Director James Comey revealed Thursday he immediately began documenting his meetings with Donald Trump because of his concerns with the president’s “nature.”

“I was honestly concerned he might lie about the nature of our meeting, so I thought it important to document,” Comey told the Senate Intelligence Committee in testimony Thursday morning.

In April, the New York Times reported that Comey began writing down his interactions with the president after a January 6 meeting at Trump Tower. “I felt compelled to document my first conversation with the President-Elect in a memo. To ensure accuracy, I began to type it on a laptop in an FBI vehicle outside Trump Tower the moment I walked out of the meeting,” said Comey’s prepared opening statement for the committee, which was released on Wednesday.

On Thursday, Sen. Mark Warner (D-VA) pressed Comey on what led him to start keeping a paper trail of his meetings with the president. Here’s Comey’s full account:

A combination of things. I think the circumstances, the subject matter, and the person I was interacting with. Circumstances, first — I was alone with the president of the United States, or the president-elect, soon to be president. The subject matter I was talking about, matters that touch on the FBI’s core responsibility, and that relate to the president — the president-elect personally — and then the nature of the person. I was honestly concerned he might lie about the nature of our meeting so I thought it important to document. That combination of things I had never experienced before, but had led me to believe I got to write it down and write it down in a very detailed way.

Now, it’s not surprising that Comey in particular would document his private interactions with Trump. Trump’s consistent elisions of the truth have been obvious to many for more than a year. But hearing the former FBI director directly castigate the sitting president’s character was remarkable nonetheless.

Comey would again question the president’s motives later in his testimony. During a meeting on February 14, Trump asked everyone to clear out of the room except for Comey. According to the former FBI director, some of the other officials in the room — including Attorney General Jeff Sessions and Jared Kushner, the president’s senior adviser and son-in-law — seemed taken aback by the request.

“My sense was the attorney general knew he shouldn't be leaving, which was why he was lingering. And I don't know Kushner well, but I think he picked up on the same thing,” Comey said. “So I knew something was about to happen that I needed to pay very close attention to.”