The FBI had repeatedly briefed the White House last year about a senior aide to President Donald Trump who has now publicly been accused of domestic violence.
Rob Porter, 40, resigned as staff secretary a week ago after being accused of abuse by two ex-wives, which he denies.
But Christopher Wray, the FBI Director, contradicted the White House version of events surrounding background checks into Mr Porter.
The White House had said the FBI background checks into Mr Porter, carried out so he could have high level security clearance, were "on-going" and "not complete" and that senior officials only became aware of the allegations against him last week.
But Mr Wray, giving evidence to the Senate intelligence committee, said the FBI completed a partial background report last March, and a full one by late July.
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Despite that Mr Porter had continued to work with only temporary security clearance.
Mr Wray said he could not detail publicly exactly what information was given to the White House about Mr Porter.
He said: "I can’t get into the content of what was briefed to the White House. What I can tell you is that the FBI submitted a partial report on the investigation in question in March. And then a completed background investigation in late July.
"Soon thereafter, we received request for follow-up inquiry, and we did the follow-up, and provided that information in November and then we administratively closed the file in January."
Mr Wray said he was "confident" the FBI followed proper protocol in investigating Mr Porter.
After the allegations against Mr Porter first became public last week the White House issued a series of statements supporting him.
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It also emerged that he had been dating Hope Hicks, the White House communications director. When a photograph of one of his ex-wives with a black eye then became public he resigned.
Dan Coats, the Director of National Intelligence, said the US government’s system of security clearances for top officials was "broken" and must be completely overhauled.
He said: "We have a broken system and I think everybody’s come to agree with that now."
He said the process should take advantage of new technologies and information on social media to provide "early awareness of individuals".
Mr Trump voiced support for Mr Porter last week, publicly thanking him for his service and wishing him good luck in his career.
In a tweet on Saturday Mr Trump lamented that "people’s lives are being shattered and destroyed by a mere allegation".
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Sarah Sanders, the White House press secretary, later said what had been considered a final report from the FBI had been received in November.
But the White House personnel security office, staffed by career officials, had not yet made a recommendation by the time Mr Porter resigned, so the process had still been "on-going".