WASHINGTON (Reuters) -Marc Short, who was a top staffer to Republican former Vice President Mike Pence, on Monday confirmed he had testified before a federal grand jury investigating the Jan. 6, 2021, attack on the U.S. Capitol and efforts to overturn the 2020 presidential election.

“I did receive a subpoena for the federal grand jury and I complied with that subpoena,” Short told CNN. He declined to provide any details on his testimony.

ABC News first reported that Short, who served as Pence’s chief of staff, had testified on Friday afternoon. Both ABC’s cameras and Reuters cameras captured footage of Short leaving the federal courthouse in Washington, D.C., alongside his attorney Emmet Flood.

Short is the most high-profile official known to have appeared before the grand jury, which is also probing the effort by former President Donald Trump’s allies to submit slates of fake electors to overturn the 2020 election.

Short’s appearance is a sign the U.S. Justice Department’s investigation into the attack on the Capitol and the fake elector plot is heating up.

In the interview with CNN, Short said it was unfair to characterize the pro-Trump mob as simply exercising their First Amendment free speech rights.

“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 who were merely expressing their First Amendment rights,” he said.

Short said although the Secret Service wanted to evacuate Pence from the Capitol, where he was preparing to certify the presidential election results, the vice president wanted to stay.

“The vice president didn’t want the image of a 15-car motorcade fleeing the hallmark of democracy for the world to see,” he told CNN.

In an interview with CNN earlier this year, Deputy Attorney General Lisa Monaco confirmed the Justice Department had received referrals about slates of alternative fake electors that were sent to the National Archives, and said prosecutors were reviewing them.

Copies of the phony electoral slates submitted to the National Archives by pro-Trump Republicans in Arizona, Georgia, Michigan, New Mexico, Nevada, Pennsylvania and Wisconsin were made public in March by the non-profit watchdog group American Oversight, which obtained them through a public records request.

The Office of the Federal Register, part of the National Archives, coordinates some functions of the Electoral College between the states and Congress, including receiving the certificates from the states that identify their electors and receiving the certificates of votes by the electors.

The fake elector plot has featured prominently in multiple hearings of the Democratic-led U.S. House of Representatives committee probing the attack on the U.S. Capitol.

Rusty Bowers, the Arizona state House Republican speaker, testified in June that Trump and his close aides, including his personal lawyer Rudy Giuliani and adviser John Eastman, urged Bowers to reject the election results.

In recent months, the U.S. Attorney’s office in Washington, D.C., has started issuing grand jury subpoenas to electors, including some who signed the bogus certificates.

According to one subpoena seen by Reuters that is focused on the phony slate of electors in Georgia, investigators are seeking copies of documents from October 2020 related to “any effort, plan or attempt to serve as an elector in favor of Donald J. Trump and/or Mike R. Pence.”

They are also seeking copies of communications between would-be electors and any federal government employees, any employees or agents of Trump, as well as communications with a long list of people including Giuliani and Eastman.

Arizona’s Republican party chair, Kelli Ward, and her husband, Michael Ward, who both signed their names on one of the slates of alternate electors for Trump, have also received subpoenas.

    Alexander Kolodin, an attorney for the Wards, told Reuters earlier this month that the DOJ’s investigation is “based on allegations that our clients engaged in core First Amendment-protected activity, namely petitioning Congress for redress of grievances.”

(Reporting by Sarah N. Lynch and Tim Ahmann in Washington and Karen Freifeld in New York; Editing by Scott Malone and Leslie Adler)

---