The FBI is not recommending criminal charges be brought against Hillary Clinton over the use of her private email server while secretary of state, Director James Comey said Tuesday.
There was no evidence that Clinton or her aides intended to violate any laws over the handling of classified information, but "there is evidence they were extremely careless," Comey said in outlining the FBI's extensive investigation and findings.
The decision about whether or not to charge Clinton is ultimately up to prosecutors at the US Justice Department, but Comey said he believed the investigation did not turn up information that a reasonable prosecutor would use to pursue charges.
Clinton's exclusive use of a private email server has cast a cloud over her presidential election campaign, and while Tuesday's announcement largely lifts the threat of prosecution, it still painted a picture of carelessness that will continue to haunt her campaign.
The findings included 113 emails that contained classified information at the time they were sent and should not have been transmitted over her personal server, Comey said.
"Any reasonable person in Secretary Clinton's position or those with whom she was corresponding should have known the system was no place for those conversations," Comey said.
The use of the private server also opened Clinton up to hacking by foreign governments or hostile actors and it was "possible" that they could have gained access to the email, he said.
There was no clear, direct evidence that her system had been hacked, but given the sophistication of hackers it is possible they would not have left traces of their presence, he said.
He outlined a painstaking investigation that was like reconstructing a jigsaw puzzle that had been dumped onto the floor as experts trawled through servers and devices that had been decommissioned.
Clinton had turned over the bulk of the emails to the State Department in 2014, but investigators also found thousands of mails that were not handed over. Comey said there was no evidence those mails had been held back in an effort to conceal information.
Clinton was interviewed by the FBI for three and a half hours on Saturday as part of the probe.
Attorney General Loretta Lynch last week sought to reassure the public that the probe would not be tainted by political bias after she met private with former president Bill Clinton.
Lynch said she will follow the recommendations of the FBI and Justice Department prosecutors.
A State Department review released in May faulted Clinton for her exclusive use of the private email server during her tenure as secretary of state, saying the practice posed a security risk and did not comply with government records laws.
Republicans have pointed to the issue to raise questions about Clinton's trustworthiness and judgement as she runs for president and to raise the spectre of the scandals that plagued her husband Bill Clinton's presidency.