Washington(CNN) The Justice Department inspector general's report released Monday amounted to a massive fact-finding that shaded in contours of the Russia investigation.
In some ways, its new details answered questions that special counsel Robert Mueller didn't touch in his own report on how Russia interfered in the 2016 election.
For a close reader, the Horowitz report offers the backstory behind some of Mueller's work. And it's packed with juicy details about Trump campaign affiliates and investigators' efforts to understand their motivations and actions.
Here are some of the revelations from Inspector General Michael Horowitz's review:
When investigators applied for a FISA warrant against Carter Page in October 2016, they mentioned his past connections to Russian intelligence officers. But investigators didn't mention that Page "had been approved for operational contact" with those Russians by a US government agency, and that he had provided information to the US government about those Russians, according to the report.
Horowitz thought the information would have been relevant in Page's surveillance application -- though the FBI didn't mention it.
Page apparently became somewhat more comfortable, speaking to prosecutors five times during their investigation in March 2017.
During one of the interviews, he told them that in in mid-October 2016, "while crossing a street in New York City, his cell phone fell out of his pocket and was smashed by a car, resulting in a loss of encrypted communications."
Horowitz took the time to note how small a world it can be.
Steele knew Ivanka Trump "for some years," Horowitz noted in his report -- though he left out her name and referred to her only as a "Trump family member." The pair was close enough that Steele had once given her a Scottish family tartan, Horowitz noted.
Anti-Trump text messages have peppered Horowitz's investigations into the Russia investigation -- and Trump has grasped onto them as evidence of political bias (of which Horowitz said there was none).
But the inspector general noted Monday the political support among FBI officials went both ways. One FBI agent messaged another after Trump won the Presidency in 2016 that it was like "watching a Superbowl comeback," for instance.
The Mueller report was conspicuously silent on some efforts to verify the Steele dossier. But Horowitz took the opportunity to write dozens of pages about Steele's work and the FBI's trips abroad to speak with him and his primary source and to track their findings on the dossier's allegations.
Notably, the FBI never verified the existence of video tapes of "alleged unorthodox sexual activity," according to the report.
When Office of the Director of National Intelligence briefed the Trump campaign about Russian counterintelligence in 2016, the FBI had an investigator in the room watching for what then-Trump adviser Michael Flynn said, the report said. Flynn was under investigation, and so the FBI agent documented in a memo details from the briefing that could have been relevant to the Crossfire Hurricane investigation.
The agent told Horowitz he was watching Flynn to gain some familiarity with how he acted normally. Flynn later lied to investigators in the early days of the Trump administration, when he served as national security adviser, and pleaded guilty to that crime -- so the episode ultimately was useful, Horowitz noted.
The Horowitz report cites several ways the FBI botched its application to surveil the former Trump campaign adviser Carter Page, and ways it could improve the process -- much of which the FBI is working on fixing.
But one situation sticks out, and received a full narrative retelling by Horowitz: A lower-level FBI attorney adding to an email the assertion that Page was not a source for an intelligence agency. That false information got sent along in the FBI's documentation behind its FISA application, and the attorney allegedly changed his story when investigators questioned him.
It was already well-known that George Papadopoulos and Page had interacted with FBI informants in 2016. But there was one more high-ranking Trump campaign official who intersected with an intelligence informant about Russian interference in the election.
The meeting didn't reel in much useful information to the FBI. The official wasn't named in Monday's report.
The Washington Post reported last year campaign adviser Sam Clovis met with an FBI source, and Clovis himself had spoken publicly about the meeting.