Still a Jan. 6 mystery: Who placed the pipe bombs the night before the Capitol attack?

On the evening of Jan. 5, 2021, on a sleepy street a short distance from the the attack on the U.S. Capitol on U.S. Capitol, a mysterious figure loomed.

Wearing a sweatshirt with the hood pulled up, a pair of Air Max Speed Turf shoes with a yellow Nike logo, a backpack and gloves, the suspect walked through alleyways and equipped with what investigators say were two pipe bombs.

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About 7:30 p.m., the figure placed one outside the Democratic National Committee, grainy surveillance video released by the FBI shows. The suspect then walks through the residential streets behind the Capitol and places another pipe bomb outside the Republican National Committee.

"They would have exploded. They could have exploded," Steven D'Antuono, assistant director in charge of the FBI's Washington Field Office told ABC News Chief Justice Correspondent Pierre Thomas Tuesday. "They are viable devices that could have gone off and exploded, causing a lot of serious injury or death."

Just who the suspect is has vexed the FBI. A full year later, the agency still has not caught the person who placed the bombs nor has it released information about a "person of interest."

In fact, because of the way the suspect is covered up, investigators can't say for sure whether it is a man or a woman.

On a normal night, a person wearing a hood, a face covered with a mask would raise suspicions, but because of COVID-19, the person blended in, D'Antuono said.

"It's still a priority for us, has always been a priority since day one to find this individual, and we haven't stopped since the day that we found the devices," he continued.

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The FBI has done over 900 interviews on the case alone, they have collected 39,000 video files and 400 tips regarding the identity of the suspect, D'Antuono said.

The FBI and ATF are offering a reward of $100,000.

Investigators are keying in on the mannerisms of the suspect, specifically looking at the way the suspect walks.

"Please give us a call," he said. "The fascinating thing right now, we're not clear on whether this a man or woman."

They also believe the person is not from the Washington, D.C., area.

The bombs were discovered on Jan. 6 -- as Vice President Mike Pence was presiding over the congressional count of the 2020 electoral votes and the riot was developing -- adding to the confusion and chaos of the day.

Investigators initially thought it was a diversion tactic, but that notion was shot down by the FBI.

Out of the more than 700 charged in the Capitol insurrection, this case has proved to be the most frustrating for FBI senior leaders.

"This person laid or planted two viable explosive devices in a residential and commercial area that could have done people harm," he said. "We want to catch this person before they do someone else harm."