Former U.S. President Donald Trump speaks during a rally in Cullman, AL.

Marvin Gentry | Reuters

Matthew Calamari Jr., the Trump Organization’s director of security and son of its chief operating officer, is expected to testify Thursday before a Manhattan grand jury investigating former President Donald Trump’s company, a person with direct knowledge of the matter told CNBC on Wednesday.

Calamari Jr. was served a subpoena for his testimony earlier this week, the person said.

The person declined to be named in order to discuss the secret grand jury proceedings.

The development in the ongoing investigation comes two months after the Trump Organization and its chief financial officer, Allen Weisselberg, were charged in connection with an alleged tax-avoidance scheme spanning 15 years. Weisselberg and the Trump Organization have pleaded not guilty.

Calamari Jr.’s testimony could grant him crucial immunity protections in the wide-ranging and long-running criminal investigation by Manhattan District Attorney Cyrus Vance Jr.’s office.

The office of New York Attorney General Letitia James is also probing Trump’s company “in a criminal capacity.”

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A spokesman for Vance’s office declined to comment. The Trump Organization did not immediately respond to a request for comment on the testimony.

The Wall Street Journal, which first reported Wednesday that Calamari Jr. is expected to testify this week, also reported that senior Trump Organization finance official Jeffrey McConney is expected to go before the grand jury this week as well.

The prosecutors are looking at how Calamari Jr. reported on his taxes an apartment he received from Trump’s company, the Journal reported.

McConney prepared the personal tax returns of Matthew Calamari Sr., according to the newspaper.

The elder Calamari has reportedly come under scrutiny by prosecutors over whether he violated tax rules when he received benefits from the company.