Washington - The FBI won't recommend criminal charges against Hillary Clinton for her use of a private email server while secretary of state, agency Director James Comey said on Tuesday, lifting a major legal threat to her presidential campaign.Comey said that although the investigation found "extremely careless" behaviour by Clinton and her staff in their handling of sensitive information, the FBI had concluded that "no charges are appropriate". He said the agency believed that "no reasonable prosecutor would bring such a case".The announcement came three days after the FBI interviewed Clinton for hours in a final step of its yearlong investigation into the possible mishandling of classified information.Attorney General Loretta Lynch said last week that she would accept the recommendations of the FBI director and of career prosecutors, meaning that Comey's decision almost certainly brings the legal part of the issue to a close and removes the threat of criminal charges.However, it's unlikely to wipe away many voters' concerns about Clinton's trustworthiness. And it probably won't stop Republican presidential candidate Donald Trump, who has called for criminal charges, from continuing to make the server a campaign issue.Clnton's personal email server, which she relied on exclusively for government and personal business, has dogged her campaign since The Associated Press revealed its existence in March 2015.She has repeatedly said that no email she sent or received was marked classified, but the Justice Department began investigating last summer following a referral from the inspectors general for the State Department and the intelligence community.The scrutiny was compounded by a blistering audit in May from the State Department's inspector general, the agency's internal watchdog, which said that Clinton and her team ignored clear warnings from department officials that her email setup violated federal standards and could leave sensitive material vulnerable to hackers. Clinton declined to talk to the inspector general, but the audit said that she had feared "the personal being accessible" if she used a government email account.The Clinton campaign said agents interviewed her this past Saturday for three-and-half hours at FBI headquarters. Agents had earlier interviewed top Clinton aides including her former State Department chief of staff, Cheryl Mills, and Huma Abedin, a long time aide who now is the vice chair of Clinton's campaign.Lynch on Friday said that she would accept whatever findings and recommendations were presented to her. Though she said she had already settled on that process, her statement came days after an impromptu meeting with Bill Clinton on her plane in Phoenix that she acknowledged had led to questions about the neutrality of the investigation.