US Justice Department investigators say they have not found any evidence yet that the rioters who ransacked the US Capitol last week intended to capture and kill any lawmakers.

In an Arizona court filing on Friday in the case of Jacob Chansley, federal prosecutors took back an earlier assertion that supporters of President Donald Trump planned to "capture and assassinate elected officials" in the January 6 siege of the US legislature.

The claim was made in arguments to prevent the court from granting bail to Chansley, aka Jake Angeli, seen worldwide in photographs bare-shirted wearing a horned headdress and carrying a spear inside the Capitol.

But on Friday the Arizona prosecutors withdrew that claim as the Justice Department said that, despite calls during the attack to capture certain lawmakers and to kill Vice President Mike Pence, no evidence had been found yet to support any serious effort to do so.

"There is no direct evidence at this point of kill-capture teams and assassination," Michael Sherwin, the federal district attorney for Washington DC who is overseeing the investigation of the Capitol attack, told reporters Friday.

Nevertheless, the US Capitol remained on heavy lockdown Saturday ahead of the January 20 inauguration of Joe Biden as president, with security officials worried of potentially violent attacks on the event.