F.B.I. officials on Thursday released new details of their investigation into the still-unidentified suspect believed to have placed pipe bombs in Washington the night before the Jan. 6, 2021, riot at the Capitol, hoping to spur tips that might solve a lingering mystery.

The suspect, wearing a mask, a gray hooded sweatshirt, dark pants and Nike Air Max Speed Turf sneakers, put two homemade bombs outside the Democratic and Republican national party headquarters the night before the formal congressional ceremony acknowledging Joseph R. Biden Jr. had won the 2020 election.

Neither device exploded, but their discovery that morning added to the fear and confusion on a day when a pro-Trump mob stormed the Capitol, briefly delaying the certification of the results.

Now, four years later, with investigators still uncertain of the suspect’s gender, the F.B.I. has offered video from a new angle of the suspect planting a bomb near a bench outside the Democratic headquarters.

Investigators also say the suspect’s height has been estimated at 5-foot-7. There is a $500,000 reward for information leading to an arrest and conviction. The bureau refrained from releasing a height estimate until now because officials did not want to dissuade any potential tipsters, since witnesses often significantly err when guessing someone’s height.