Donald Trump Jr. spent about five hours Thursday answering questions from Senate Judiciary Committee staff about a meeting he set up between his father’s presidential campaign and a Russian lawyer, but the details beyond his opening statement remain private for now.

Several senators attended the closed-door, voluntary interview with the president’s son, part of the committee’s probe into possible Russian interference in the 2016 presidential election. Only Senate staffers asked questions, however, and the committee will have to vote at a later time on whether to make the transcript public.

A committee aide said that transcript process could take “a while.”

Sen. Richard Blumenthal, one of the most outspoken critics of President Donald Trump, declined to comment about the substance of the interview when he left the interview room. Although not classified, the members of the committee had agreed not to speak publicly about the interview, the Connecticut Democrat said.

Senators who attended included Democrats Richard J. Durbin of Illinois, Amy Klobuchar and Al Franken of Minnesota, Sheldon Whitehouse of Rhode Island and Blumenthal, as well as Republican Sen. Orrin G. Hatch of Utah. Judiciary Chairman Charles E. Grassley of Iowa did not attend.

Blumenthal described Thursday’s interview as “cordial,” indicated that the younger Trump answered questions, and said he expects him to come back and testify at a public committee hearing.

“There’s still a lot of questions that need to be covered,” he said. “There certainly are a lot of areas that have been opened for future witnesses and questioning and a lot of areas of interest to be pursued.”

Coons, in an interview later Thursday with MSNBC, said one question he hopes to ask the president’s son in an open session is how an e-mail suggests Trump Jr.’s “response to being told that [Russian President Vladimir] Putin and Putin’s regime were trying to help his father win the election wasn’t surprise, wasn’t ‘I need to report this,’ but was instead, ‘Great, let’s go ahead with the meeting.’”

Coons also sent news media a copy of a memo pointing out that anyone who testifies in front of a Senate committee is under the restrictions of the False Statements statute. The Delaware Democrat added that “material false statements to Congress are criminal and punishable with fines or imprisonment or both.”

Blumenthal said a copy of Trump Jr.’s opening statement Thursday, first obtained by The New York Times, appeared to be similar to the statement the president’s son delivered to Senate investigators.

In the statement, Trump Jr. said he was initially conflicted when he heard that the Russian lawyer might have damaging information about Democratic nominee Hillary Clinton, the Times reported.

Trump Jr. said in the statement that he always intended to consult with his own lawyers about using any information given to him at the June 2016 meeting at Trump Tower in New York City, according to the Times.

“To the extent they had information concerning the fitness, character or qualifications of a presidential candidate, I believed that I should at least hear them out,” Trump Jr. said in the statement. “Depending on what, if any, information they had, I could then consult with counsel to make an informed decision as to whether to give it further consideration.”

The Judiciary Committee’s probe is one of several congressional investigations about possible collusion between the Trump campaign and the Russian government to influence the 2016 election.

A special counsel, Robert S. Mueller III, continues his own investigation and has amassed a team of experienced lawyers for the task.