Robby Mook, Hillary Clinton’s former campaign manager, said he was unaware who funded the so-called “Trump dossier,” which contains scandalous and unverified material on Trump's ties to Russia, amid reports that Clinton’s campaign and the Democratic National Committee paid the firm that eventually hired the dossier's author.

"I didn't know that we were paying the contractor that created that document," Mook told CNN's Anderson Cooper on Friday.

"When we started to look into Donald Trump's business dealings, it was this massive tree of LLCs and shell companies,” he added. “We were overwhelmed, we were on it, frankly.”

"I asked our lawyer and I gave him a budget allocation to investigate this, particularly the international aspect. My understanding is that the dossier is the product of not just research that funded by our campaign, but also by Republican donors," he said.

The opposition research firm was was referring to was Fusion GPS, which began conducting opposition during the Republican primaries for the conservative Washington Free Beacon, the Washington Examiner reported last week. Then, during the summer of 2016, the firm was retained by lawyer Mark Elias, who represented the Clinton campaign and the Democratic National Committee.

Fusion GPS paid former British intelligence officer Christopher Steele’s company, Orbis Business Intelligence, $168,000 for the work that led to the Trump dossier.

Democrats, including Clinton officials, deny having any direct connection to the research that amounted to the Trump dossier.

Some aspects of the dossier — like communications between foreign nationals — have been confirmed by officials; however, the majority of the scandalous allegations included in the document have not been verified.

The dossier came to light publicly after it was published in full by BuzzFeed in January.