Special counsel Robert Mueller is reportedly questioning how much President Donald Trump knew about his son Donald Trump Jr.’s 2016 meeting with Kremlin-linked lawyers at Trump Tower and if the president sought to hide the purpose of that meeting, NBC reports.

“Even if Trump is not charged with a crime as a result of the statement, it could be useful to Mueller’s team to show Trump’s conduct to a jury that may be considering other charges,” an unnamed source told NBC.

Trump Jr. was invited to meet with a Russian lawyer on the promise that she could provide him with incriminating information about then-presidential rival Hillary Clinton, but he later said the talks centered on the Magnitsky Act (a 2012 law that allowed the U.S. to withhold visas and freeze Russian assets) and a subsequent Russian ban on adoptions by Americans.

Mueller issued grand jury subpoenas in early August to learn more about the meeting as part of his investigation into possible collusion between the Trump campaign and Russia to help Trump win the presidency.