The House select committee investigating the January 6 Capitol attack is moving to capitalize on new momentum as it embarks on its final push to complete the roughly one hundred remaining depositions and conclude the evidence-gathering phase of the inquiry.

The panel has scored two major wins in recent days: more than six hours of testimony from Donald Trump’s son-in-law and adviser Jared Kushner, and a conclusion by a federal judge that the former president committed felonies to overturn the 2020 election.

Members on the select committee believe Kushner’s cooperation might prompt other Trump officials to assist the investigation as the panel inches closer to Trump’s inner circle and the former president himself, according to sources familiar with the matter.

The panel has also been buoyed by the federal court ruling that said Trump “more likely than not” violated the law over 6 January, reaffirming the purpose of the investigation and making it harder for Trump’s allies to defy the inquiry, the sources said.

And members on the select committee believe that opening contempt of Congress proceedings against the Trump aides Peter Navarro and Dan Scavino for ignoring their subpoenas, will reinforce the message that the panel will punish non-compliance, the sources said.

“There’s a momentum to this process when there’s cooperation,” Jamie Raskin, one of the congressmen on the panel, said of the burst of recent activity. “When people see that others are doing the right thing, it gives them the courage to do the right thing.”

The select committee has now conducted more than 800 depositions and interviews, obtained almost 90,000 documents and followed up on more than 435 tips received through the tip line on its website, since it started its work in earnest last August.

House investigators also have more than 100 depositions remaining on the schedule, the sources said, including one with a key witness who is expected to reveal connections between the Oath Keepers and the Proud Boys militia groups and the Capitol attack.

That deposition – slated for 5 April – would represent another breakthrough and could play a big role in establishing for the select committee whether Trump oversaw a criminal conspiracy as part of his efforts to overturn the 2020 election.

It is so crucial, the sources said, since it could form part of the evidence to connect the militia groups that stormed the Capitol to the organizers of the rallies that immediately preceded the attack – who in turn are slowly being linked to the Trump White House.

But that testimony has been on the books for several weeks, and the greater challenge for the select committee remains to resolve ongoing cooperation talks with Rudy Giuliani, Trump’s one-time attorney, and Ivanka Trump, the former president’s daughter.

The select committee has a special interest in Giuliani since he was in close contact with Trump as he oversaw the implementation of the scheme to have the thenvice-president, Mike Pence, stop the certification of Joe Biden’s election win and return Trump to office.

The Guardian first reported that Giuliani was poised to cooperate with the investigation and reveal the roles played by Republican members of Congress with caveats – such as not discussing matters covered by executive privilege – that are not yet resolved.

House investigators have also identified Ivanka Trump as a key person of interest since she appeared to have learned before 6 January that the scheme to have Pence stop the certification was unlawful – but and might shed light on why the former president still went ahead with the plan.

Testimony that speaks to whether Trump knew what he was pressing Pence to do was unlawful – and when he knew it – is a central question for the panel as it seeks to establish whether Trump’s actions should warrant a criminal referral to the justice department.

The panel has also privately noted in recent days that Ivanka Trump might be able to shed light on who Trump was calling from the White House as the Capitol attack unfolded, after call logs from that day showed a near eight-hour gap in communications.

The Guardian has revealed at least one of Trump’s phone calls on 6 January – when he dialed the Republican senator Mike Lee trying to reach Senator Tommy Tuberville – was routed through an official White House phone and should have been in the call logs but was not.

As the select committee moves towards wrapping up the evidence-gathering phase of the investigation, the hope among its members is that the recent momentum will carry the inquiry through to public hearings that are now expected to start in mid-May.

The panel remains undecided whether to demand cooperation from Ginni Thomas, the wife of the supreme court justice Clarence Thomas, after the Washington Post and CBS reported she pressed Trump’s former chief of staff Mark Meadows in texts to overturn the 2020 election.

The issue centers on the fact that several members on the select committee did not know about Thomas’s texts – turned over by Meadows months ago – until news reports brought them to public attention, according to two sources familiar with the matter.

Some members wanted to call her in to ask her about the texts, but others who had discussed the issue months ago demurred, arguing that Thomas, a far-right activist, was unlikely to assist the panel and would try to turn the inquiry into a political circus.

A spokesperson for the panel did not respond to a request for comment.

The select committee may yet request cooperation from Thomas, but House investigators are pursuing myriad lines of inquiry and whether to ask her for voluntary assistance or demand documents and testimony pursuant to a subpoena is just one strand, the sources said.