Former FBI agent Peter Strzok helped write the controversial letter to Congress sent by then-FBI Director James ComeyJames Brien ComeyBook: FBI sex crimes investigator helped trigger October 2016 public probe of Clinton emails Trump jabs at FBI director over testimony on Russia, antifa Graham: Comey to testify about FBI's Russia probe, Mueller declined invitation MORE announcing the reopening of the probe into Democratic presidential nominee Hillary ClintonHillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE, according to emails obtained by CNN. 

Strzok, who in 2016 sent dozens of anti-Trump text messages in what conservatives have called clear evidence of bias, co-wrote the first draft of the letter but was unsure about reopening the investigation so close to the election, sources told CNN in a report published Wednesday. 

The day after Strzok sent his draft to colleagues, Comey released the final version of the letter, bringing Clinton's emails back into the spotlight just weeks before Election Day.

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Comey reopened the investigation that October, when thousands of emails of Clinton's surfaced on the laptop of former aide Huma Abedin's husband Anthony Weiner in a separate investigation. 

Clinton and top Democrats have said the letter was a key factor in her election loss to President TrumpDonald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE.

Comey has said that it made him "mildly nauseous" to think that reopening the Clinton probe may have swayed the election, but that he would have made the same decision again.

Strzok later went on to work on the Justice Department's probe into possible collusion between the Trump campaign and Russia, but was removed by special counsel Robert MuellerRobert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE after the politically charged texts he exchanged with an FBI lawyer were revealed.

Trump and congressional Republicans say the texts are evidence that the probe into the Trump campaign is biased, while Democrats say they are trying to undercut Mueller's credibility. 

Trump accused Strzok of "treason" in a Wall Street Journal interview earlier this month.

Strzok also reportedly edited a key line in Comey's statement in July 2016 originally announcing Clinton would face no charges over her "home brew" server. He changed the phrase "grossly negligent" to "extremely careless" in regards to her actions.