The Democratic congressman from Mississippi said if any witnesses resist, he was willing to use the panel’s subpoena authority “to the fullest extent of the law.”

He said the panel hired professional staff to obtain a vast amount of data and will continue to do so through the summer break. The panel held a strategy meeting Wednesday where Thompson told his colleagues that, “whatever recess you might have planned for August, you might have to reassess it.”

For more reporting from the Associated Press, see below.

Thompson says the committee hopes to “set the tone” of the investigation by hearing from first responders, many of whom were brutally beaten by former President Donald Trump’s supporters as they pushed past law enforcement and broke into the Capitol. The rioters screamed at officers and verbally abused them as they fought their way inside and interrupted the certification of President Joe Biden’s victory. The Jan. 6 panel held an initial strategy session this week,

“We need to hear how they felt, we need to hear what people who broke into the Capitol said to them,” Thompson told the Associated Press in an interview Friday. “And so we want to frame that first hearing so that everybody would know the committee is serious, but also that we take those individuals who either secure the Capitol or clean the Capitol—that we care about them.”

Thompson said the select committee is eyeing the week of July 19 for the hearing, which is likely to be a dramatic curtain-raiser for the new investigation. An increasing number of police officers who responded to the attack, including members of the Capitol Police and Washington’s Metropolitan Police Department, have lobbied for Congress to launch an independent investigation of the insurrection, but the proposal was blocked by Senate Republicans. The officers have pressured Republicans who have downplayed the violence to listen to their stories, and several watched from the gallery last week as the House voted along party lines to form the select committee.

Two Senate committees have already investigated the attack and made security recommendations, but they did not examine the origins of the siege, leaving many unanswered questions.

House Speaker Nancy Pelosi has appointed eight members to the select committee, including seven Democrats and Republican Rep. Liz Cheney of Wyoming. Republican Leader Kevin McCarthy has discretion over five additional appointments, though Pelosi must approve them.

McCarthy has not yet said who he will appoint or if Republicans will even participate in the probe, as many in the party are still loyal to Trump and have sought to downplay the insurrection and deny the political motives behind it.

Thompson said the panel welcomes Republican members but will be moving ahead regardless of whether McCarthy chooses to participate. Under the committee’s rules, only eight members are required for the committee to have a working quorum. He said a lack of GOP participation won’t diminish what the committee is trying to do.

“As chair, my role is to keep the committee moving forward, making sure that whatever deflections that come up basically would not impede the work of the committee. And I plan to do that.”

Thompson said the central focus of the investigations will be why the systems that were in place that day failed—why there wasn’t a greater presence of law enforcement, why the military was delayed for hours as the police were quickly overwhelmed and why crucial intelligence predicting the attack was missed.

The panel is also expected to probe the links that some rioters had to white supremacist groups. Thompson said an assessment by FBI Director Christopher Wray that racially motivated violent extremism, and especially white supremacy, is one of the biggest threats to U.S. security, coupled with the insurrection, “tells me that the significance of this committee’s work is as important as it can ever get.”

The committee is still deciding how much of its work will be done behind closed doors, Thompson said, as some witnesses may not want to testify in public and some information could be sensitive or classified.

He said there will also be no foregone conclusions—on timing or otherwise—as the committee begins its work.

“We don’t have a timetable,” Thompson said. “The goal of the committee is to be as thorough as we can in the investigation, but also flexible to the point that we know that things change along the way.”