Peter Strzok, a former top counterintelligence expert at the FBI, was responsible for former FBI Director James Comey's language in July 2016 describing Hillary Clinton's handling of classified information as "extremely careless," according to U.S. officials familiar with the matter.

Strzok, the second-ranking official in the FBI's counterintelligence division, helped lead the investigation into Clinton's private email server and was responsible for changing Comey's earlier draft language. Comey originally called Clinton's handling of classified information "grossly negligent," but Strzok then changed the language to "extremely careless," according to CNN:

The drafting process was a team effort, CNN is told, with a handful of people reviewing the language as edits were made, according to another US official familiar with the matter. The shift from "grossly negligent" to "extremely careless," which may appear pedestrian at first glance, reflected a decision by the FBI that could have had potentially significant legal implications, as the federal law governing the mishandling of classified material establishes criminal penalties for "gross negligence." Senate Judiciary Chairman Chuck Grassley, R-Iowa, raised questions over why the change was made after receiving documents from the FBI last month, but the identity of who was behind the edit has not been reported until now.

"Although we did not find clear evidence that Secretary Clinton or her colleagues intended to violate laws governing the handling of classified information, there is evidence that they were extremely careless in their handling of very sensitive, highly classified information," Comey said during a statement to the press. "There is evidence to support a conclusion that any reasonable person in Secretary Clinton’s position, or in the position of those with whom she was corresponding about these matters, should have known that an unclassified system was no place for that conversation."

CNN also learned it was Strzok who signed off on a document to officially open an investigation into Russia meddling in the 2016 presidential election, according to sources familiar with the agreement.

The New York Times reported Saturday that special counsel Robert Mueller removed Strzok from his Russia investigation during the summer. The Justice Department's inspector general began an investigation into whether the agent sent text messages attacking President Donald Trump, prompting him to be reassigned to the FBI's human resources department.

He was reassigned after it was discovered he and a colleague exchanged multiple texts reacting to news events, including presidential debates, in a manner that could be construed as critical of Trump and his political views.

The Times went on to note Mueller acted swiftly and made the transfer after it was revealed there could be potential bias by one of his agents.

Trump has called the Russia investigation a "witch hunt" multiple times.