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A former top counterintelligence expert at the FBI, now at the center of a political uproar for exchanging private messages that appeared to mock President Donald Trump, changed a key phrase in former FBI Director James Comey’s description of how former secretary of state Hillary Clinton handled classified information, according to US officials familiar with the matter.

Electronic records show Peter Strzok, who led the investigation of Hillary Clinton’s private email server as the No. 2 official in the counterintelligence division, changed Comey’s earlier draft language describing Clinton’s actions as “grossly negligent” to “extremely careless,” the sources said.

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.

RELATED: Source explains why Comey didn’t use ‘grossly negligent’ to describe Clinton

CNN has also learned that Strzok was the FBI official who signed the document officially opening an investigation into Russian meddling in the 2016 election, according to sources familiar with the matter. As the No. 2 official in counterintelligence, Strzok was considered to be one of the bureau’s top experts on Russia.

But the news of Strzok’s direct role in the statement that ultimately cleared the former Democratic presidential candidate of criminal wrongdoing, now combined with the fact that he was dismissed from special counsel Robert Mueller’s team after exchanging private messages with an FBI lawyer that could be seen as favoring Clinton politically, may give ammunition to those seeking ways to discredit Mueller’s Russia investigation.

The FBI and the Justice Department declined to comment.

CNN reported in November that Comey and his FBI colleagues were “playing with the language” throughout the process of drafting Comey’s statement on Clinton, believing that they needed to condemn the former secretary of state’s handling of classified information, while also making clear they would not recommend criminal charges, according to a source familiar with the FBI decision.

Comey ultimately called Clinton’s conduct “extremely careless,” but said “no reasonable prosecutor” would pursue charges based on the evidence.

“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 back in July 2016.

Grassley said that documents the FBI provided to the Senate Judiciary Committee in November included an earlier draft of Comey’s exoneration statement from May 2016, which stated: “There is evidence to support a conclusion that Secretary Clinton, and others, used the private email server in a manner that was grossly negligent with respect to the handling of classified material.”

Grassley then asked for the electronic “metadata,” which would include “who created the original drafts, who made the edits to the draft statement, and when those edits were made.”

Sources familiar with the requests tell CNN that Grassley has received the metadata, but he wants the FBI to provide further explanation about the changes.

Grassley’s office did not return a request for comment.

CNN’s Pamela Brown contributed to this report.