#CNN: More than 120 people were accused of organizing riots on January 6

Federal investigators leading the probe into the January 6 Capitol riot briefed interim Biden administration leaders at the Justice Department on Wednesday -- their first day on the job -- as the sprawling nationwide hunt for suspects continues, an official briefed on the matter said.

Prosecutors have charged more than 120 people, as of Thursday, and have taken steps to bring more serious charges, including charging a group of alleged attackers with conspiracy. The charges range from unlawfully entering the US Capitol grounds to assaulting police -- and a few defendants face more serious counts of conspiracy or threatening a public official.

The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives on Wednesday increased the reward to $75,000 for tips about the pipe bombs found near the Capitol on the day of the attacks -- a sign that investigators are still struggling to identify the perpetrators.

That elusiveness may indicate the person or people behind the bombs were more sophisticated in their operation, a law enforcement official said. Investigators have looked through hours of surveillance video and combed through cellphone site data to try to find those responsible.