WASHINGTON (AP) — A key email from Hillary Clinton to a top State Department aide in 2010 expressing worry that her personal messages could become "accessible" to outsiders is cited in a new inspector general's report on her emails. But Clinton did not turn over that particular email, which was later obtained by the investigators.

U.S. Democratic presidential candidate Hillary Clinton speaks at Transylvania University in Lexington, Kentucky, U.S., May 16, 2016. Reuters/Aaron Bernstein A key email from Hillary Clinton to a top State Department aide in 2010 expressing worry that her personal messages could become "accessible" to outsiders is cited in a new inspector general's report on her emails. But Clinton did not turn over that particular email, which was later obtained by the investigators.

The presumptive Democratic presidential nominee was supposed to have turned over all work-related emails to the State Department for public release. That public release was supposedly completed at the end of February.

But the agency's watchdog found three emails never seen before by the public, including Clinton's explanation for why she wanted her emails kept private — "I don't want any risk of the personal being accessible," one of Clinton's emails read in November 2010 — and details of hacking attempts on her personal computer server, written by her former IT director in January 2011.

The existence of these previously unreleased messages — which appear to have been found among electronic files of four former top Clinton State Department aides — renews concerns that Clinton was not completely forthcoming when she turned over a trove of 55,000 pages of work-related emails. And it has drawn fresh criticism from presumptive Republican presidential nominee Donald Trump.

Clinton's physical server is currently being investigated by the FBI.

Clinton first admitted to exclusively using a private email account to send and receive work-related emails while she served as secretary of state in March 2015. The controversy compelled her to hand over roughly 30,000 work-related emails to the State Department, which have been released in batches since last year.

But she deleted about 30,000 additional emails from her server that she says were "personal" in nature before handing it over to the FBI in August, five months after handing over individual emails to the State Department.

U.S. Democratic presidential candidate Hillary Clinton greets supporters at Transylvania University in Lexington, Kentucky Thomson Reuters

Around the time she handed over the server, a House committee requested access to it to ensure that she had not deleted any work-related emails. But her lawyer, David Kendall, told the committee that Clinton aides had changed the server's settings so that only emails she sent and received in the previous 60 days would be saved.

An inspector general's report released Wednesday on email practices within the State Department faulted Clinton and previous secretaries of state for poorly managing email and other computer information, and for slowly responding to new cybersecurity risks.

The report cites "longstanding, systemic weaknesses" related to communications that precede Clinton's appointment as secretary of state. The State Department singled out Clinton's failures as "more serious," however, according to the Associated Press.

"At a minimum, Secretary Clinton should have surrendered all emails dealing with department business before leaving government service and, because she did not do so, she did not comply with the Department's policies that were implemented in accordance with the Federal Records Act," the report reads.