The freshman New York lawmaker has said he's not a "criminal."
The FBI has contacted a Navy veteran, Richard Osthoff, as part of an investigation into embattled Rep. George Santos and a GoFundMe campaign to raise money for Osthoff's sick service dog.
Osthoff confirmed the call from the FBI, and sources familiar with the matter confirmed the nature of the investigation -- which adds to the growing list of legal issues and controversies Santos, R-N.Y., is facing.
The freshman lawmaker insists he isn't a "criminal" and has said he will leave office if he isn't reelected. He has acknowledged and apologized for lying about parts of his background while maintaining that he was only embellishing his resume.
According to previous ABC News reporting, a source familiar said Santos, using the name Anthony Devolder, ran a GoFundMe account in 2016 under the auspices of a charity, Friends of Pets United, and raised some $3,000 to ostensibly help Osthoff pay for surgery to remove a tumor from his dog.
Osthoff told ABC News that Santos did not come through with the money and ignored text messages about it. Osthoff says his dog, Sapphire, ultimately died from her condition.
"I don't ever want to see another person, especially another veteran, go through this again," Osthoff said.
Santos' campaign previously described Friends of Pets United as a 501(c)(3) nonprofit, but IRS records do not list a charity under that name.
Santos told ABC News on Wednesday that he was unaware of the FBI probe and said of Osthoff, "I have no recollection of ever meeting him." Osthoff previously provided a local news outlet with texts that he said were between him and Santos.
When asked if he was worried about being prosecuted, Santos responded, "I have no clue, I don't know what it's about."
He also told ABC News he had not been contacted by anyone regarding the investigation. "I haven't been reached out by them. So I can't comment," he said.
Federal prosecutors in Brooklyn are investigating Santos, including the charity, which is also part of an investigation by the New York attorney general's office, according to sources familiar with both investigations.
Spokespeople for both the U.S. attorney's office for the Eastern District of New York and the FBI's New York field office declined to comment on the ongoing investigation.
The FBI outreach to Osthoff was first reported by Politico.
In December, as reports emerged about Santos fabricating some of his life story, he told The New York Post that he was sorry for "embellishing" but said: "This (controversy) will not deter me from having good legislative success. I will be effective. I will be good."