WASHINGTON — Paul Manafort, President Trump’s former campaign chairman, spread a conspiracy theory now at the center of the impeachment investigation — that Ukraine, not Russia, hacked the Democratic National Committee — as early as five months before the 2016 election, according to newly released documents from the special counsel’s investigation.

Mr. Manafort told his deputy on the campaign about the theory shortly after emails stolen from the Democrats were published in June 2016, and questions arose about whether Russia hacked the emails to help the Trump campaign, according to the documents.

The documents have no information about when Mr. Trump embraced the conspiracy theory, which he later asked Ukraine’s president to investigate in a July 25 phone call even as he was withholding military aid for the country. Those revelations helped touch off the impeachment inquiry.

The details of what Mr. Manafort told campaign officials are included in a trove of records from the special counsel’s investigation obtained by BuzzFeed News through a Freedom of Information Act lawsuit. The documents — including F.B.I. interview reports with several key witnesses and emails of Mr. Trump’s top campaign officials — contain few startling details that were not in the report by the special counsel, Robert S. Mueller III, but they underscore the notion that Mr. Trump’s campaign eagerly welcomed Russia’s help in the election and show how concerned campaign officials were about being tied to Russia.