(BBC) – Republicans in the US Senate have blocked a bill to establish a bipartisan commission to investigate the Capitol Hill riot.
The measure passed the US House of Representatives last week.
Members of ex-President Donald Trump’s party said the riot is already being investigated by congressional panels.
Democrats argued that forming a commission, similar to the one created after 9/11, would prevent any repeat of a similar invasion on the Capitol.
Trump supporters stormed Congress on 6 January in a failed bid to overturn the certification of President Joe Biden’s victory in November’s election.
The riot left five dead, including a Capitol police officer.
Although 54 senators, including six Republicans, voted in favour of creating the commission, the bill failed.
It needed 60 votes due to a rule called the filibuster where 60 of the 100 senators must vote in favour of a bill for it to pass.
Speaking from outside an ice cream parlour in Ohio on Thursday, Mr Biden condemned Republicans, saying: “I can’t imagine anyone voting against establishing a commission on the greatest assault since the Civil War on the Capitol.”
Also before the vote, the mother of police officer Brian Sicknick – who died a day after the attack from a stroke – visited Capitol Hill along with her son’s girlfriend, Sandra Garza, to lobby lawmakers to support the commission.
“Not having a January 6 Commission to look into exactly what occurred is a slap in the faces of all the officers who did their jobs that day,” said Gladys Sicknick.
She suggested that any members of Congress opposed to the bill should visit her son’s grave in Arlington National Cemetery, just outside the US capital.
Investigators say Mr Sicknick was targeted by a rioter with some kind of chemical spray, though a post-mortem examination found he died from natural causes.
More than 440 suspected participants in the attack have been arrested and officials say they expect to charge another 100.
The investigation is one of the most extensive ever undertaken by the Department of Justice, and the number of cases has overwhelmed the Washington DC court system.
Several of those arrested were police officers, and dozens were military veterans. The defendants face charges including trespassing in a federal building, violent entry and disorderly conduct.