(CNN) The forthcoming release of an internal Justice Department watchdog report on the FBI's Trump-Russia investigation won't be the last word on the matter, Attorney General William Barr has told conservative allies.

Long a skeptic of the Russia probe, and particularly the FBI's tactics to investigate Trump campaign associates, Barr believes questions remain about some of the intelligence and other information the FBI used to pursue the investigation, according to people at the Justice Department and in Congress familiar with his thinking.

That view stands in contrast to what is expected from Justice Inspector General Michael Horowitz's report, due to be released next Monday, which is expected to conclude that the FBI's investigation was legally predicated , despite errors and potential wrongdoing by some lower-level FBI employees involved in it, CNN reported last month.

"The inspector general's investigation is a credit to the Department of Justice," said Kerri Kupec, Justice Department spokeswoman. "His excellent work has uncovered significant information that the American people will soon be able to read for themselves. Rather than speculating, people should read the report for themselves next week, watch the inspector general's testimony before the Senate Judiciary Committee, and draw their own conclusions about these important matters."

Long before Horowitz's report was complete, Barr had already decided the inspector general's review wouldn't be enough to answer some of his concerns, some of which he has made public.

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