What we know about 'Unindicted Co-conspirator #1' in the indictment against the Trump Organization and its CFO

• A 15-count indictment against the Trump Organization and its CFO was unsealed Thursday.
• Prosecutors reference an "Unindicted Co-conspirator #1" in the document.
• This person had a role in determining CFO Allen Weisselberg's compensation in 2009, according to the indictment.
• See more stories on Insider's business page.

There is an anonymous person lurking in the background of the New York grand jury indictment against the Trump Organization and CFO Allen Weisselberg unsealed Thursday: "Unindicted Co-conspirator #1."

Twice in the 25-page document, prosecutors reference the unindicted co-conspirator. Prosecutors normally use the term to refer to someone involved in an investigation who may still face charges down the line.

The charging document refers to only one unindicted co-conspirator.

According to the indictment, the Trump Organization, Allen Weisselberg, and the unindicted co-conspirator "agreed to and implemented" a compensation scheme that allowed Weisselberg to underreport his income. Prosecutors allege this scheme permitted Weisselberg to claim tax refunds he wasn't entitled to, and skip out on paying taxes on $1.7 million worth of income since 2005.

"As a result of the conspirators' actions, during the period of the conspiracy, Weisselberg took approximately $94,902 from the United States Internal Revenue Service in federal tax refunds to which he was not entitled," the charging document says.

More specifically, the indictment says that the unindicted co-conspirator played a role in underreporting Weisselberg's income from 2009.

"On or before April 5, 2010, the Trump Corporation, acting through its agent, Unindicted Co-conspirator #1, underreported Allen Weisselberg's taxable income for the tax year 2009," the indictment says.

So, who is it?

All we know so far is that, according to prosecutors, it's someone who would be in a position to underreport Weisselberg's taxable income in 2009.

• That could be Donald Trump himself. After all, Trump was the CEO of the Trump Organization in 2009, and it stands to reason that he would sign his CFO's checks.
• It could also be someone like Jeffrey McConney, the Trump Organization controller. He has worked for the Trump Organization since 1987, according to his LinkedIn, and in his role has a deep understanding of the company's finances and payroll. McConney reportedly testified before the grand jury in June, and therefore may be legally protected from any charges based on his testimony, depending on whether he made an arrangement with the District Attorney's office before testifying.
• It could also be another tax preparer. The Trump Organization used Mazars USA, a third-party tax firm that handed over copious documents to the DA's office after being subpoenaed. Given how closely intertwined the Trump Organization's finances are with its executives' finances, it's possible Mazars accountants worked on Weisselberg's personal taxes as well.
• Or maybe it's a third-party accountant who prosecutors allege was complicit in Weisselberg's scheme to misrepresent his income for tax purposes in 2009.

Trump has repeatedly dismissed the investigation as a politically-motivated "witch hunt." McConney and a representative for Mazars didn't immediately respond to Insider's request for comment.

In federal charges against a different Trump Organization executive, Michael Cohen, for illegal hush-money payments given to Stormy Daniels, prosecutors referred to an "Individual #1" later determined to be then-President Trump himself.

That case triggered the Manhattan District Attorney's investigation into the Trump Organization's finances. The grand jury ultimately brought 15 charges in what prosecutors described as a sweeping tax-fraud scheme.

Weisselberg and attorneys for the Trump Organization pleaded not guilty to the 15 counts in court Thursday.

Prosecutors have been pressuring Weisselberg to cooperate in the investigation, and he may still do so even after Thursday's charges. If the CFO does cooperate, it is likely prosecutors will ask for information about Trump's personal role in preparing the Trump Organization's tax forms and determining executive compensation.