Rep. Zoe Lofgren described the radio broadcast, the existence of which was not previously known, during a House Administration Committee hearing on security failures around the January 6 attack.
In that transmission, the officer said: "Attention all units on the field, we're not looking for any pro-Trump in the crowd. We're only looking for any anti pro-Trump who want to start a fight," according to Lofgren, a California Democrat.
Lofgren, who chairs the committee, said she was quoting from an account of the radio call, which was found by the Department Office of Professional Responsibility during its ongoing review of allegations related to officer conduct on January 6. She did not identify the officer.
A Capitol Police spokesman told CNN the radio communication described occurred around 8 a.m. the day of the riot. The spokesman added that the communication was meant to guide officers to also look for clashes between pro-Trump protesters and counterprotesters. The official who made the comment is not under investigation, the spokesman said.
Neither Capitol Police nor Congress has released the audio of the broadcast, despite requests to do so.
US Capitol Police Inspector General Michael Bolton said he had not yet read internal reports from the investigation -- which CNN reported last month involves allegations against 36 officers -- but planned to do so once the review was completed.
A committee aide told CNN that Lofgren's line of questioning underscores the point that the USCP, based on the available intelligence at the time, had ample reason to expect violence from pro-Trump protestors directed at the Capitol and lawmakers but "despite this and all the rhetoric online ... USCP supervisors on the morning of 1/6 were apparently still advising their front line officers to focus on and prioritize anti-Trump protesters."
Going forward, Bolton "will be able to review the radio transmissions, and he plans to review the findings in general and command and control communications, knowing now that there's a specific allegation about those communications he should specifically look at it," the aide said.
Lofgren's description of the radio broadcast in question offers some rare insight into the kind of conduct from Capitol Police that is being looked at as part of the ongoing probe.
A department spokesperson told CNN in February
that six US Capitol Police officers had been suspended with pay for their actions in the January 6 riot. Of the 36 officers under investigation from January 6, 23 of the cases are complete. Thirteen of the cases remain under investigation, a department spokesperson told CNN last month.
One of the suspended officers took a selfie with someone who was part of the mob that overtook the Capitol, Rep. Tim Ryan, an Ohio Democrat, said at the time. Another wore a "Make America Great Again" hat and started directing people around the building, Ryan added.
Acting USCP Chief Yogananda Pittman said in January that the department "has been actively reviewing video and other open source materials of some USCP officers and officials that appear to be in violation of Department regulations and policies."
This story has been updated with comments from a Capitol Police spokesman.