Late Friday and early Saturday, law enforcement officials said there was no chance the email review could be completed before Election Day. By Sunday, officials said they would spare no resources in the investigation and try to determine whether the new emails changed the Justice Department’s conclusion not to charge Mrs. Clinton or her aides.

The emails will be reviewed by the same counterintelligence team in Washington that handled the Clinton investigation from the beginning. The review will focus on whether there is evidence in the emails that Ms. Abedin mishandled classified information or impeded the F.B.I.’s original email investigation.

Investigators will also want to know whether the new trove includes messages that Ms. Abedin did not turn over to the F.B.I. months ago. Ms. Abedin has said she did not routinely delete emails, and people close to her said she did not know these emails were on Mr. Weiner’s computers. It is not clear how they got there, but it is possible they were automatically backed up.

The Justice Department efforts were described by three federal law enforcement officials who spoke on the condition of anonymity because they were not authorized to discuss the case.

The F.B.I. knew weeks ago that its investigation into whether Mr. Weiner sent illicit text messages to a 15-year-old girl in North Carolina had the potential to reignite the Clinton case. After agents seized Mr. Weiner’s laptop, phone and tablet on Oct. 3, they quickly learned the computer contained a trove of Ms. Abedin’s emails.

The assistant F.B.I. director in charge of the New York field office then notified the deputy director in Washington about the discovery, according to one senior law enforcement official. Agents in the Weiner case were not allowed to widely search Ms. Abedin’s emails, but were told to conduct a cursory review of the metadata — the “to” and “from” information on each message — to see if any of the emails could be relevant to the Clinton investigation.