Facebook was aware of the data misuse by the UK political consultancy Cambridge Analytica as early as September 2015, three months earlier before the scandal was originally revealed by an exclusive story of the Guardian. 

An internal email chain, released on Friday, shows Facebook employees raised alarms in September 2015 that the now-defunct Cambridge Analytica and other third parties were using its data in ways that may violate its policies. 

The message chain starts when a Facebook staff wrote that they had been hearing an increasing number of allegations that various firms had been "scraping" user information from its service and matching them to voter registration files. 

"The largest and most aggressive on the conservative side," they write, "is Cambridge Analytica, a sketchy (to say the least) data modeling company that has penetrated our market deeply." 

They asked for technical help in investigating "what Cambridge Analytica specifically is doing". The investigation then appeared to falter, and the discussion moved onto other firms before the Guardian's story on December 11 broke out. 

In his testimony to the U.S. Congress last April, Facebook CEO Mark Zuckerberg said that Facebook had first learned about Cambridge Analytica's misconduct of improperly collecting user data in December 2015. 

The new documents appear to contradict that claim, although the e-mails seem to be written by low to mid-level employees. 

The documents were jointly released by Facebook and District of Columbia Attorney General Karl Racine. 

“The District of Columbia fought to make this document public because we believe the American people have a right to know what and when Facebook knew about its data security weaknesses," a spokesperson for Racine’s office said. 

Facebook had its worst privacy scandal in years following allegations that the Trump-affiliated data-mining firm Cambridge Analytica used ill-gotten data from millions of users through an app to try to influence elections. 

The social media giant was fined a record-breaking five billion U.S. dollars by the U.S. Federal Trade Commission in July for its mishandling of user data.