The special counsel Robert Mueller will testify before Congress about the findings of the Russia investigation on 24 July, one week later than his appearance was originally planned, under an agreement that gives lawmakers more time to question him.

Mueller had been scheduled to report on the inquiry into Russian election meddling and ties between Russia and the campaign of Donald Trump on 17 July. But lawmakers in both parties complained that the short length of the hearings would not allow enough time for all members to ask questions.

Under the new arrangement, Mueller will testify for an extended period of time, three hours instead of two, before the House judiciary committee. He will then testify before the House intelligence committee in a separate hearing. The two committees said in a statement that all members of both committees will be able to question him.

In the joint statement, the panels said the longer hearing “will allow the American public to gain further insight into the special counsel’s investigation and the evidence uncovered regarding Russian interference in the 2016 presidential election and President Trump’s possible obstruction of justice and abuse of power”.

Mueller has expressed his reluctance to testify and said he will not go beyond what is in his 448-page report. But Democrats have been determined to highlight its contents for Americans who they believe have not read it. They want to extract information from the former special counsel and spotlight what they say are his most damaging findings against Trump.

Democrats are expected to ask Mueller about his conclusions, including that he could not exonerate Trump on obstruction of justice after detailing several episodes in which Trump tried to influence the investigation. Mueller also said there was not enough evidence to establish a criminal conspiracy between Trump’s presidential campaign and the Kremlin.

One thing judiciary members want to focus on in questioning Mueller is whether Trump would have been charged with a crime were he not president. Mueller said at the news conference that charging a president with a crime was “not an option” because of longstanding justice department policy. But Democrats want to know more about how he made that decision and when.

The committees did not say whether expected closed-door sessions with two of Mueller’s deputies, James Quarles and Aaron Zebley, would go on. Those sessions, part of an original deal struck between Congress and the deputies, appeared to be in doubt after the justice department recently pushed back on the arrangement.

It is unclear whether Mueller’s testimony will give Democratic investigations new momentum. In the news conference, Mueller indicated that it was up to Congress to decide what to do with his findings. But Democrats have had little success so far in their attempts to probe his findings as the White House has blocked several witnesses from answering questions.

That means the committees may have to go through a lengthy court process to get more information. About 80 Democrats have said they think an impeachment inquiry should be launched to bolster their efforts, but the House speaker, Nancy Pelosi, has so far rebuffed those calls.