(CNN) Facebook originally proposed trekking to the Hill in the middle of the August recess, a traditionally quiet time when much of Washington is on vacation, but that idea was immediately met with pushback from Hill investigators who argued nobody would be in town, sources said Friday.

Facebook officials were overruled by Hill investigators, who said the tech giant would have to reveal its findings on the Russian purchase of ads during the 2016 election when Congress returned in September, one source familiar with the discussions said.

A second source familiar with the matter said that mid-August was floated not to downplay the findings, but because that's when Facebook said it was first prepared to talk with Congress. When Facebook officials finally did show up to the Hill Wednesday, they revealed the bombshell that a Russian "troll farm" linked to the Kremlin had purchased $100,000 worth of ads -- some of which appear designed to plug Facebook users into streams of fake news and Russian propaganda.

For Facebook, and Hill investigators, it was a stunning new revelation just months after the company said it had discovered no evidence of Russian operatives buying ads on its platform.

But US intelligence officials have been tracking Russia's efforts to push propaganda and fake news over social media for years. And the FBI, specifically, was aware of the Russian ad buys well before Facebook revealed them to congressional investigators, two US officials said.

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