A major investigation into Hillary Clinton's use of a private email server while she was secretary of state found no evidence of deliberate mishandling of classified information.

The finding by the U.S. State Department, released on Friday by Republican Senator Chuck Grassley's office, follows a three-year investigation, for which Clinton handed over roughly 33,000 emails.

Assertions of wrongdoing had been a major cornerstone of President Donald Trump's 2016 election campaign—with repeated chants and demands to "lock up crooked Hillary"—however, Trump made no mention of the findings on Friday.

The investigation was launched by Grassley in 2017 when he was chairman of the Senate Judiciary Committee.

Senator Chuck Grassley (R-IA), speaks during a Senate Judiciary Committee hearing with on Capitol Hill on June 11, 2019. Grassley has been one of Hillary Clinton's most ardent critics with regards to use of a private email server while she was Secretary of State.Getty

Grassley remained critical of Clinton's handling of classified information after it was revealed she had been using a private email to conduct official business when she was the top U.S. diplomat from 2009 to 2013.

The Iowa Republican pressed on with his investigation despite then-FBI Director James Comey stating in 2016 that he would not recommend any criminal charges. Comey did, however, criticize Clinton's use of a private email server as "extremely careless."

The Justice Department's inspector general also said that FBI specialists had not found evidence that the server was hacked.

This latest report concluded there was "no persuasive evidence of systemic, deliberate mishandling of classified information."

Despite that, 38 unidentified people were said to be "culpable" in 91 cases after sending classified information which made its way to Clinton's personal email.

Those cases were part of 588 violations that were found from the 33,000 emails, however, fault could not be determined in the remaining 497 cases.

For those found culpable, the violations will be noted in their files and will be considered when applying for or renewing security clearances. It may also mean some form of disciplinary action for those still employed by the State Department, however, it was not clear what that action would be.

The report said "that the use of a private email system to conduct official business added an increased degree of risk of compromise as a private system lacks the network monitoring and intrusion detection capabilities of state department networks," reported AP.

Clinton herself was cleared of any mishandling of classified information and "by and large, the individuals interviewed were aware of security policies and did their best to implement them in their operations."

President Donald Trump, left, and former Secretary of State Hillary Clinton. Trump called for Clinton to be "locked up" for use of a private email server, however, a new report clears Clinton of any wrongdoing.Getty

In September, after it emerged that the State Department had reportedly "intensified" its investigation and retroactively recategorized some of the emails as classified, Clinton told NowThis she believed that the investigation was a "witch hunt."

"My reaction, as you might predict, was absolute bewilderment and disappointment," she said.

"My understanding from press coverage is that [the State Department] are talking to 130 people. These people are experienced foreign service officers and other distinguished Americans that have had great careers.

"What does it mean to retroactively classify something they've sent?

"It's a witch hunt. And it's a real one unlike the kinds of things Trump talks about."

Newsweek has contacted representatives for Clinton, the White House and the State Department for comment.