WASHINGTON — Shortly after Hillary Clinton was interviewed on Saturday by agents at the F.B.I.’s headquarters, its director, James B. Comey, heard from his deputies that Mrs. Clinton had been truthful and forthcoming in the three-and-a-half-hour meeting.

Mr. Comey, who had been regularly briefed on the progress of the yearlong investigation into Mrs. Clinton’s email account as secretary of state, had known for some time that his agents had not uncovered enough evidence to charge her or anyone else with a crime. Now, with the interview done, he told his deputies, according to F.B.I. officials, that he wanted to move forward with a plan he had been working on for months to explain the findings from such a politically contentious investigation to the public. And he did not wait to do it.

At 11 a.m. on Tuesday, Mr. Comey walked into a conference room on the first floor of the F.B.I.’s headquarters, where he stood behind a lectern for 15 minutes and laid out in clinical detail how Mrs. Clinton’s use of the account was “extremely careless.” But, he said, the bureau would recommend to the Justice Department that she not be charged with a crime because his investigators had found no clear evidence that Mrs. Clinton had intentionally broken the law.

The careful approach to publicly explaining his thinking fit a pattern for Mr. Comey, who, throughout his three decades as a law enforcement official, has refused to shy away from politically fraught issues. While he was immediately praised by some for his candor and transparency, it did not insulate him from criticism from both Republicans and Democrats, as well as some legal experts.