Federal investigators working for Special Counsel Robert Mueller are keenly focused on President Donald Trump’s role in crafting a response to a published article about a meeting between Russians and his son Donald Jr., three sources familiar with the matter told NBC News.

The sources told NBC News that prosecutors want to know what Trump knew about the meeting and whether he sought to conceal its purpose.

The meeting occurred at Trump Tower in June 2016 and was attended by Donald Trump Jr., Trump campaign chairman Paul Manafort, and Trump’s son-in-law Jared Kushner. The meeting, which was first reported by The New York Times, also involved Russian attorney Natalia Veselnitskaya and former Soviet intelligence officer Rinat Akhmetshin.