Of the many questions that surround Representative George Santos, one has recently taken center stage: Who guaranteed the $500,000 bond that allowed him to be released from federal custody last month?

Mr. Santos, 34, and his lawyer have for weeks attempted to thwart efforts to make public the names of his guarantors, at one point claiming to the court that Mr. Santos — who awaits trial on 13 federal criminal charges — would rather go to jail than have them revealed and subjected to public scrutiny.

But the mystery surrounding Mr. Santos’s bond is expected to be resolved at noon Thursday, after a federal judge in the Eastern District of New York dismissed his appeal to keep the names sealed.

Some of the wilder theories about the source of the bail funds were seemingly put to rest. In court filings opposing the disclosure of the so-called sureties, Mr. Santos’s lawyer, Joseph Murray, all but declared that Mr. Santos’s guarantors were relatives.

Mr. Santos has asserted that his guarantors would withdraw their support if their identities were to be revealed, which would mean Mr. Santos would have until noon on Thursday to ask to change the conditions of his bond. He may include a request to keep the newly withdrawn guarantors under seal. But any changes would require discussion with federal prosecutors and could include pretrial detention, though former prosecutors say it is unlikely.

The identities of Mr. Santos’s guarantors attracted immense interest after reporting by The New York Times and other outlets exposed falsehoods in his biography and raised ethical questions regarding his personal and campaign finances.

Mr. Santos, who represents parts of Long Island and Queens, has admitted to lying about his education and work history. But he has not addressed other inconsistencies and has equivocated when asked about his business dealings and how they related to his political efforts.

Federal prosecutors accused Mr. Santos of orchestrating a scheme to solicit political contributions that he used for personal expenses; of fraudulently receiving more than $24,000 in pandemic unemployment benefits while he was actually employed; and of knowingly making false statements on House financial disclosure forms.

Mr. Santos was charged with wire fraud, making unlawful monetary transactions and theft of public funds and pleaded not guilty to all charges.

Still, many questions remain. The House Ethics Committee, which has been investigating Mr. Santos for months, asked that he disclose the names of his sureties so it could determine whether the bail guarantee violated House rules regarding gifts. Media organizations, including The Times, asked the court to release the guarantors’ identities, arguing that their names were a matter of public interest.

In attempting to block that effort, Mr. Murray shared with the court a letter he wrote to the Ethics Committee in which he argued that Mr. Santos had not violated its rules. He cited an exception that allows representatives to receive gifts or favors from immediate relatives, spouses, extended family or in-laws.

Mr. Murray was more explicit in a subsequent court filing, saying that Mr. Santos had “essentially publicly revealed that the suretors are family members and not lobbyists, donors or others seeking to exert influence over the defendant.”

Mr. Santos’s immediate family includes his younger sister, Tiffany, who donated thousands of dollars to her brother’s campaign despite owing tens of thousands of dollars in back rent in Queens. She also served as the president of a New York State PAC called Rise NY, which has ties to Mr. Santos and whose handling of funds has raised questions.

Mr. Santos’s father, Gercino dos Santos Jr., lives in New York. In past contributions to his son’s congressional campaign, he listed his occupation as either a painter or in construction, or noted that he was retired. Mr. Santos has also said that he married in November 2021, and has said his husband was a pharmacist named Matheus Gerard.

Mr. Santos earlier this month lost his request to keep sealed the identities of the people who guaranteed his bond. He subsequently filed an appeal that was dismissed by Judge Joanna Seybert on Tuesday. The next hearing on his case is scheduled for June 30.

Nicholas Fandos contributed reporting.