The FBI told a federal judge that it needed to search a computer to resume its investigation of Hillary Clinton's use of a private email server because agents had found correspondence on the device between Clinton and top aide Huma Abedin but they did not know what was being discussed, according to newly unsealed court documents.

The bureau argued that Clinton and Abedin were previously on email chains in which classified information was discussed, and so there was probable cause to search a computer belonging to Abedin's estranged husband, disgraced former Anthony Weiner, for information potentially related to the Clinton email case. That search - along with the FBI Director James Comey's decision to tell Congress that the investigation into Clinton's email practices had resumed - came less than two weeks before the election and upended the presidential campaign.

U.S. Magistrate Judge Kevin Nathaniel Fox approved a search warrant in the case, but the FBI is likely to draw criticism that it relied on flimsy evidence to resume its Clinton probe.

E. Randol Schoenberg, the Los Angeles lawyer who sued to have the warrant unsealed, said he saw "nothing at all in the search warrant application that would give rise to probable cause, nothing that would make anyone suspect that there was anything on the laptop beyond what the FBI had already searched and determined not to be evidence of a crime, nothing to suggest that there would be anything other than routine correspondence between Secretary Clinton and her longtime aide Huma Abedin."

"I am appalled," Schoenberg said.

The FBI and a lawyer for Abedin declined to comment for this story. A lawyer for Clinton did not immediately return a message.

The documents largely lay out what agents had already found in the case, which FBI Director James Comey had in July declared he was recommending be closed with no charges. The agent wrote that the government had determined 2,115 emails on Clinton server were classified - 2,028 at the confidential level, 65 at the secret level and 22 at the top secret level, which is the most sensitive.

The agent wrote that 27 email chains containing classified information went through Abedin accounts: six contained information classified secret at the time it was sent, and 21 was classified confidential. The agent wrote that - given thousands of Abedin emails were found on the computer belonging to Weiner, including some that appeared to have been sent while Clinton was secretary of state - there was probable cause to believe their correspondence contained classified information.

At the time the agent applied for the warrant, the FBI was working on limited information. Agents were reviewing the laptop in the context of the Weiner investigation and could look at header information, but could not look at the contents of emails belonging to Abedin because they were outside the scope of their authority to search. Weiner's and Abedin's names are redacted from the newly released documents, but they were confirmed by a person familiar with the case.

Edward MacMahon, a white-collar defense attorney who has handled high-profile cases involving classified information, said he believed agents seemed to have acted appropriately in obtaining the warrant to search Weiner's computer.

"Look, probable cause is such a low standard," MacMahon said. "The way I read this is they're saying they found another computer that may have had additional emails on it, and they wanted to search that computer. That's completely consistent with what the FBI would want to do in a case like this."

Comey wrote to Congress on Oct. 28, two days before the FBI obtained the warrant, to announce agents were resuming their work on the Clinton email case. Agents in an "unrelated case," he wrote, had found emails that "appear to be pertinent to the investigation." Law enforcement officials, speaking on the condition of anonymity, soon revealed that case was the investigation of Weiner's alleged sexting with a 15-year-old girl, and on Oct. 30, the FBI obtained the warrant to look more thoroughly at Weiner's computer for Clinton-related materials.

U.S. District Judge P. Kevin Castel unsealed the warrant and related documents at the request of Schoenberg, a lawyer specializing in art theft cases. Schoenberg sued for the materials' release, arguing that, because of the questions surrounding the Clinton email investigation and the impact of the FBI's decision to resume it on the eve of the election, the public deserved to know more. On Nov. 6, Comey announced that investigators had concluded their review and found no reason to change their earlier conclusion about Clinton.

Government lawyers initially opposed unsealing the warrant but soon dropped their objection. The FBI had already released on its website an extensive summary of its investigative efforts before the case had resumed, as well as dozens of interview summaries with witnesses in the case. Clinton took no position on the release of the warrant.

Matt Zapotosky covers the Justice Department for the Washington Post's National Security team.
@mattzap