Christopher A. Wray, the F.B.I. director, appeared on Wednesday before Congress, fielding a barrage of questions about how a gunman nearly killed former President Donald J. Trump.
“The attempted assassination of the former president was an attack on our democracy,” Mr. Wray said during his opening statement.
The F.B.I. is investigating the shooting on July 13 at a campaign rally for Mr. Trump in Butler, Pa. The shooting left Mr. Trump’s ear bloodied, killed a rallygoer who had been sitting in the stands and seriously injured two others.
Secret Service snipers killed the gunman, Thomas Crooks, 20, after locating him on a nearby roof. Mr. Crooks was armed with an AR-15-style rifle and had magazines for the rifle and a bulletproof vest in his car.
So far, the F.B.I. has not a found a motive for the shooting. But the bureau continues to examine the gunman’s electronic devices looking for additional clues about Mr. Crooks’s mind-set and movements beforehand.
It is not clear what other information the F.B.I. might release during the hearing before the House Judiciary Committee, but the bureau has been forthcoming with details about the shooting since Mr. Crooks is dead. While the F.B.I. typically does not discuss continuing investigations, the extraordinary circumstances and public interest in the failed assassination attempt allow the bureau to inform the public.
Lingering questions remain about the gunman’s violent trajectory and when he actually started to plan the shooting.
The F.B.I. has conducted more than 100 interviews, and scores of bureau personnel are involved in the investigation.
During testimony before Congress on Monday, Kimberly Cheatle, the head of the Secret Service, faced withering questions from both sides of the political aisle, repeatedly declining to answer questions about the security lapses that led to the assassination attempt.
Officials investigating the matter, including lawmakers in hearings this week, have repeatedly questioned why the Secret Service’s security perimeter did not include the building from which the gunman eventually fired and why no law enforcement officer was stationed there during the rally. They have also asked why Mr. Trump was allowed to take the event stage when law enforcement, including the Secret Service and the local police, was searching for a suspicious person.
On Tuesday, in the face of mounting calls that she step down, Ms. Cheatle resigned.
Mr. Wray is not expected to face the same level of criticism since the F.B.I. was not directly involved in protecting the president on July 13, but he could have other details about an Iranian plot to kill Mr. Trump or other national security threats.
In the hearing on Monday with Ms. Cheatle, the chairman of the House Intelligence Committee, Representative Michael Turner of Ohio, said that Mr. Wray was shocked that information about the Iranian threat was not included in the Secret Service threat assessment for Mr. Trump’s rally in Butler.