The unnamed employee said he was called into a meeting last year under the guise of a promotion and found himself in front of Facebook's investigative team armed with proof he'd been leaking to the press.
"It's horrifying how much they know," the employee told The Guardian. "You go into Facebook and it has this warm, fuzzy feeling of 'we're changing the world' and 'we care about things'. But you get on their bad side and all of a sudden you are face to face with [Facebook CEO] Mark Zuckerberg's secret police."
The investigative team, headed by Sonya Ahuja — confirmed by her LinkedIn profile — had records of screenshots the employee had taken and links he had visited or even just hovered over.
The investigators also indicated they had records of chats between the employee and a journalist.
"When you first get to Facebook you are shocked at the level of transparency. You are trusted with a lot of stuff you don't need access to," the employee told The Guardian. "The counterbalance to giving you this huge trusting environment is if anyone steps out of line, they'll squash you like a bug."
Facebook did not immediately respond to a request for comment from CNBC, but a company spokesperson told The Guardian, "Companies routinely use business records in workplace investigations, and we are no exception."