Warnings from US intelligence about the risk of an armed assault on the Capitol in Washington in January failed to reach police in time, a report by two Senate committees has found.
Five people died when supporters of then US President Donald Trump stormed Congress on 6 January.
The Senate report pointed to failures in communications and intelligence.
The Capitol police force was criticised as being slow and ineffective in its response to the violence.
The report does not discuss the role of the Republican president, Mr Trump, in the riots, although it does note he encouraged supporters to go the Capitol building.
Sources told US media the wording was chosen carefully to preserve bipartisan agreement between Republican and Democrat senators on the committees.
Mr Trump was impeached on a charge of inciting a mob to storm the Capitol but was acquitted in February.
The Senate report is the joint work of the Rules and Homeland Security committees.
In addition to covering the failures on the day it also sets out recommendations.
Intelligence agencies are said to have failed to properly assess the social media chatter ahead of the violence.
And on the day, the Washington DC National Guard was not deployed by the Pentagon until three hours after it was requested by police.
Among the recommendations the report makes are allowing the Capitol police chief to get a direct response from the National Guard rather than awaiting Pentagon approval.