Christopher Steele—the former British intelligence agent and author who wrote the infamous dossier that alleged misconduct between the Trump campaign and Moscow—has been interviewed by U.S. government lawyers probing the origins of the Mueller investigation, Reuters reports. Three attorneys from the inspector general’s office of the Justice Department reportedly met with Steele in Britain last month, while Trump was visiting the country. Steele’s dossier alleged that Moscow tried to help Trump’s campaign and was widely quoted for other, more salacious claims, about the president. One of Reuters’ sources said the investigators appear to have found Steele’s information sufficiently credible to extend the investigation.