Former vice-president Mike Pence’s chief of staff Marc Short appeared last week before a federal grand jury investigating events connected to the January 6 Capitol attack, indicating the justice department has penetrated the inner circle of the Trump White House in its criminal inquiry.

The appearance by Short – the top adviser to the former vice president who was also by Pence’s side on the day of the Capitol attack – makes him the highest-ranking Trump White House official known to have testified before the grand jury in Washington.

Short testified in response to a subpoena for around two to three hours, according to a source familiar with the matter, though it was unclear what he told the grand jury or whether he produced documents. ABC News earlier reported his appearance.

The development was also the latest indication that the criminal investigation into the Capitol attack has only escalated in recent months, as the House January 6 select committee argues Trump obstructed an official proceeding – a crime – in trying to stop Joe Biden’s certification.

It was not clear to which grand jury, and therefore to which investigation, Short testified. The justice department has impaneled several grand juries over the Capitol attack, including one examining Trump’s fake electors scheme, which is also being investigated by a special grand jury in Georgia.

The grand jury investigating the fake electors scheme – grand jury #22-4 – sought information about the involvement of Donald Trump and his lawyers, while the grand jury that subpoenaed former Trump White House official Peter Navarro – grand jury #22-3 – sought his contacts with Trump.

Nonetheless, Short’s grand jury appearance marks the first known time that a top Trump White House official with inside knowledge about Trump’s actions leading up to the Capitol attack and what took place in the West Wing in the following days has cooperated with the justice department.

When Short testified in a transcribed interview with the select committee earlier this year, he told congressional investigators about how Trump tried to enlist Pence in order to have him stop Biden’s certification as part of a wider effort to overturn the 2020 election results.