What did official investigations (Mueller, DOJ inspector general) conclude about the dossier's accuracy and use?

1. Mueller’s bottom line: dossier did not drive proof of a criminal conspiracy

Mueller’s investigation treated the dossier as one of many streams of information but did not find that Steele’s memos proved a criminal conspiracy between the Trump campaign and the Russian government; the special counsel’s report makes only passing references to the dossier and reached the broader conclusion that no criminal conspiracy existed as charged ^{[4] [2]}. Mueller’s team investigated lines in the dossier where they could—finding, for example, that certain sensational claims (such as a Prague meeting involving Michael Cohen) did not pan out to support criminal charges—and otherwise relied on independently obtained evidence rather than Steele’s raw memos ^{[5] [1]}.

2. Horowitz (DOJ IG): a mixed credibility picture and procedural failures

Inspector General Michael Horowitz’s review found that the Steele reporting contained both verifiable and unverifiable material, that some claims were inaccurate (including the Prague–Cohen allegation the FBI determined was untrue), and that much of the corroborated detail was limited to time, location, and titles that were often publicly available ^{[3] [5]}. Horowitz also documented that the FBI made “significant errors and omissions” when relying on the dossier in FISA applications to surveil Carter Page, raising questions about the bureau’s vetting and presentation of Steele-derived material to the FISA court ^{[6] [1]}.

3. What the FBI actually did to verify — and what that revealed

The FBI opened inquiries into virtually every line of the memos and compiled investigative work products, including spreadsheets and interviews with Steele’s primary source, which produced mixed results: agents confirmed some peripheral facts but found key, sensational allegations unsubstantiated; an FBI internal spreadsheet and agent commentary reflected skepticism, with senior officials describing parts of the dossier as “salacious and unverified” ^{[7] [8] [3]}. The IG’s review recounts fieldwork—traveling to interview Steele and his collector—and records that the primary human source told FBI interviewers much of the material was rumor and hearsay and not fact-based, further undercutting the dossier’s most explosive allegations ^{[9] [10]}.

4. Credibility debates and competing narratives remain

The inspector general’s reporting also left room for alternative readings: some accounts relayed to Horowitz suggested Steele was “sufficiently credible” at times such that investigators pursued follow-ups, and parts of Steele’s reporting did correspond with independently established events, producing a “mixed” credibility assessment rather than wholesale dismissal ^{[11] [3]}. Conversely, critics—including congressional Republicans and media commentators—seized on the errors and the DOJ IG’s findings to argue the dossier was largely discredited and improperly used to justify surveillance ^{[6] [8]}. Both strands are supported in the public record: there were verifiable kernels and investigative leads tied to the dossier, but also important inaccuracies and procedural lapses in how the FBI incorporated Steele material into court filings ^{[3] [1]}.

5. Bottom-line synthesis and limits of these official findings

Taken together, Mueller and the DOJ inspector general concluded that the dossier was not a reliable, stand-alone road map to criminal collusion—Mueller did not rely on it to prove a conspiracy—and Horowitz documented both investigative efforts to check Steele’s claims and troubling failures in how the FBI used some dossier-derived material in FISA applications ^{[2] [3] [6]}. Reporting in the sources shows that some dossier items were corroborated in narrow ways while other headline claims were disproven, but the sources available here do not exhaust every evidentiary thread or subsequent litigation, so this synthesis reflects the public parts of the official reviews cited above ^{[5] [4]}.