(CNN) — Marc Short, the former chief of staff to Vice President Mike Pence, confirmed Monday that he testified last week in front of a grand jury investigating the January 6, 2021, attack on the US Capitol in Washington, DC.

Short’s participation — which CNN reported earlier, citing a source familiar with the matter — makes him the highest profile witness known to have testified in the criminal investigation into the attack on the US Capitol. His testimony signals that prosecutors are scrutinizing the Trump White House as part of their investigation, which has expanded beyond the rioters who breached the Capitol.

“I can confirm that I did receive a subpoena for the federal grand jury, and I complied to that subpoena,” Short told CNN’s Erin Burnett on “OutFront.” “But under advice of counsel, I really can’t say much more than that.”

The New York Times and Wall Street Journal reported Monday that a second top former Pence aide, Greg Jacob, was subpoenaed in the inquiry and testified before the federal grand jury. As Pence’s general counsel, Jacob played a critical role in countering efforts to persuade the then-vice president not to certify the electoral results and was part of Pence’s team that pushed back on fringe legal theories.

Earlier this year, the Justice Department expanded its investigation beyond the rioters who breached the Capitol into fundraising and organizing for the political rally that served as a prelude to the riot as well as into efforts to subvert the Electoral College vote count.

The Justice Department has issued several subpoenas to Republican operatives connected to the scheme to put forward “alternate” electors, and the grand jury heard testimony from “Stop the Steal” organizer Ali Alexander in June.

Short and his attorney, Emmet Flood, were seen Friday leaving the federal courthouse where a federal grand jury is hearing testimony related to January 6 and to efforts to overturn the 2020 presidential election. ABC was first to report on his testimony.

Short was in a meeting at the White House two days before the Capitol attack in which Trump and lawyer John Eastman tried to persuade Pence that he had the power to stop certification of the election results.

The Justice Department did not immediately respond to a request for comment.

The House select committee, which is conducting a separate, parallel investigation into January 6, declined to comment. Short testified to the committee in January.

Earlier Monday, a video released by Democratic Rep. Elaine Luria of Virginia, who serves on the panel, showed a copy of the speech Trump gave on January 7, 2021, with edits that Ivanka Trump identified as coming from her father.

Among the lines Trump crossed out were “I am directing the Department of Justice to ensure all lawbreakers are prosecuted to the fullest extent of the law” and “Legal consequences must be swift and firm.”

Asked by Burnett about the edits Monday evening, Short said, “Certainly there were probably some people who foolishly got caught up in the events that were happening on the sixth. But I think it’s unfair to describe the rioters as patriots or merely expressing their First Amendment rights.”

This story has been updated with additional developments Monday.

The-CNN-Wire™ & © 2022 Cable News Network, Inc., a WarnerMedia Company. All rights reserved.