A Republican district attorney in New York has opened an investigation into congressman-elect George Santos, who flipped a hotly-contested congressional seat in Long Island, after he admitted to lying about his work experience and education during his campaign.

Nassau County District Attorney Anne Donnelly announced the probe as Santos faces mounting criticism from Democrats and Republicans alike over his fabrications. 

"The numerous fabrications and inconsistencies associated with Congressman-Elect Santos are nothing short of stunning," Donnelly said in a statement. "The residents of Nassau County and other parts of the third district must have an honest and accountable representative in Congress. No one is above the law and if a crime was committed in this county, we will prosecute it." 

NY REP-ELECT GEORGE SANTOS CONFESSES TO LIES ABOUT HIS RESUME: REPORT

Brendan Brosh, a spokesman for Donnelly told Fox News Digital in a statement that the DA's office was "looking into the matter."

Santos, who will represent a portion of Long Island in the House of Representatives after flipping New York's 3rd Congressional District, made the confession during an interview with the New York Post. During his congressional campaign, he falsely claimed he graduated from college with degrees in finance and worked for Goldman Sachs and Citibank. 

After an investigation by the New York Times revealed major portions of his biography were fabricated, his purported employers confirmed to Fox News that Santos never worked for them, and Baruch College said he never attended there.

In an interview with the New York Post on Monday, Santos confessed that he "never worked directly" for Goldman Sachs and Citigroup, suggesting that he probably could have used a better choice of words. Instead, Santos said, he worked for Link Bridge, which did business with both Citigroup and Goldman Sachs.

He has balked at not serving his two-year term in Congress despite calls for him to step down.

EMBATTLED GOP REP.-ELECT GEORGE SANTOS FIRES BACK AT NEW YORK TIMES AFTER BIOGRAPHY QUESTIONED

"I am not a criminal," he told the Post. "This [controversy] will not deter me from having good legislative success. I will be effective. I will be good."

Former Rep. Tulsi Gabbard, who was guest-hosting for Tucker Carlson on "Tucker Carlson Tonight," this week, asked Santos whether voters should be able to trust him after the revelations about his resume.

"I think humans are flawed, and we all make mistakes, Tulsi," he said. "I think we can all look at ourselves in the mirror and admit that once in our life we made a mistake. I'm having to admit this on national television for the whole country to see. And I have the courage to do so because I believe that in order to move past this and move forward and be an effective member of Congress, I have to face my mistakes, and I'm facing them."

Fox News Digital has reached out to Santos. 

Robert Zimmerman, the Democrat who Santos defeated in the November midterm election, said the Republican should resign and face him again in a special election. 

"George, if that's even your real name, if you're so convinced that #NY3 voters still trust you – resign & run against me again in a special election," Zimmerman tweeted Tuesday. "Face the voters with your real past & answer questions about your criminal history. Let the voters decide."

Fox News' Chris Pandolfo contributed to this report.