Trump supporters clash with police and security forces as they storm the US Capitol in Washington, DC, on January 6, 2021.Olivier Douliery/AFP via Getty Images Law enforcement agencies could have prevented the Jan. 6 attack, a committee investigator said. Tim Heaphy told NBC News that the FBI and DHS had important intel but failed to act on it. The Congressional committee investigating the attack downplayed law enforcement's role in the riot. The Federal Bureau of Investigation, Department of Homeland Security, and several other law enforcement agencies had the intelligence necessary to stop the Jan.