Federal prosecutors in Central Islip, New York, accuse Santos of engaging in a "scheme to defraud" his campaign donors.

According to the indictment, Santos solicited donations for his run for office "under the false pretense" that those funds would actually be used for politics.

Instead, prosecutors said Santos spent "thousands of dollars of the solicited funds on personal expenses, including luxury designer clothing and credit card payments."

Santos is also charged with illegally receiving unemployment benefits during the pandemic even though "he was employed and was not eligible for unemployment benefits," the indictment said.

Santos is also charged with lying to the House of Representatives on his financial disclosures. Taken together, U.S. Attorney Breon Peace said. Santos relied on "repeated dishonesty and deception to ascend to the halls of Congress and enrich himself."

Among the accusations in the charging documents are allegations that Santos applied for unemployment benefits during the pandemic, falsely claiming to have been unemployed since March 2020, according to prosecutors.

He collected money from then until April 2021, "when Santos was working and receiving a salary on a near-continuous basis and during his unsuccessful run for Congress," referring to his first run for the job, which he lost. In total, prosecutors say he collected more than $24,000 in benefits.

He was actually being paid a $120,000 salary as regional director of an investment firm at the time, according to prosecutors.

Santos left Washington, D.C., on Tuesday and drove up to New York to surrender.

Before leaving, Santos met with House GOP leader Kevin McCarthy's staff and informed them that he would be charged.

He's expected to plead not guilty, sources told ABC News.

Santos met with the FBI at an off-site location Wednesday morning and surrendered to authorities.

In one story of alleged misdeeds, as ABC News previously reported, the FBI contacted a Navy veteran, Richard Osthoff, about a GoFundMe campaign Santos established to raise money for the veteran's service dog.

Santos established the GoFundMe account under the auspices of a charity, Friends of Pets United, and raised $3,000 to help Osthoff pay for surgery to remove a tumor from the dog, sources said.

But Osthoff told ABC News Santos did not come through with the money and ignored text messages about it. The dog, Sapphire, subsequently died.

These allegations are not included in Wednesday's indictment, however.

Santos insisted earlier this year he would serve out his term despite mounting controversies surrounding his past falsehoods, scrutiny of his finances, and multiple investigations.

Santos, who has admitted to fabricating parts of his biography, has denied any criminal wrongdoing.