The newly released and uncorroborated dossier on US president-elect Donald Trump began circulating widely in Washington in October - a month before his election victory over Hillary Clinton.
Back then, Mother Jones magazine described how a former Western spy - assigned to look into Trump's Russian ties for a private American firm - had presented his findings to the FBI in August.
Those findings, the magazine said, were produced for political opposition research and said that Russian intelligence had compromised Trump during his visits to Moscow - information that, if true, could be used to blackmail him or undermine his presidency.
The Wall Street Journal on Wednesday identified the dossier's author as Christopher Steele, a director of London-based Orbis Business Intelligence.
"I don't think it would be appropriate for me to make any comments at the moment on what happened, whether Orbis has been involved or not, and we'll review that situation in the next couple of days," Christopher Burrows, co-director of Orbis, said.
Neighbour Mike Hopper said Steele had lived there for about 18 months with his wife and four children.
"He did not say where he was going or when he was coming back," he said.
CNN reported Tuesday night that Trump had been briefed in a classified setting about a summary of the investigator's findings.
Meanwhile, BuzzFeed published the 35-page dossier on Tuesday.
The website defended publishing the report because it said Americans "can make up their own minds about allegations about the president-elect."
Other news outlets withheld publishing most details about the unverified claims because they couldn't confirm them.
Shortly after reports were published late Tuesday about the dossier, Trump tweeted: "FAKE NEWS - A TOTAL POLITICAL WITCH HUNT!"
The president-elect said at a combative news conference on Wednesday that the allegations were "phony stuff" leaked by "sick people."
Director of National Intelligence James Clapper said in a statement later that he had spoken with Trump on Wednesday and told him the intelligence community "has not made any judgment that the information in this document is reliable."
Clapper also said he does not believe that the leaks came from inside the intelligence community.
"James Clapper called me yesterday to denounce the false and fictitious report that was illegally circulated. Made up, phony facts. Too bad!" Trump tweeted on Thursday.
The dossier contains unproven information about close co-ordination between Trump's inner circle and Russians about hacking into Democratic accounts as well as unproven claims about unusual sexual activities by Trump.
