When did Mueller know there was no collusion?

Finally, there was what became, in Trump accusers’ minds, Exhibit A of collusion: the Trump Tower meeting. By the end of 2017, Mueller had the testimony of most of the participants. He interviewed the translator, Anatoli Samochornov, on July 13, 2017, and participants Rinat Akhmetshin and Irakly Kaveladze on Nov. 14, 2017, and Nov. 16, 2017, respectively. Mueller did not interview Donald Trump Jr. — the report noted that the younger Trump “declined to be voluntarily interviewed” by prosecutors. But Mueller had testimony from Trump Jr. before the Senate Intelligence Committee, House Intelligence Committee, and Senate Judiciary Committee. Mueller interviewed Jared Kushner on April 11, 2018. He also had extensive documentation on the meeting from all sides, including Trump Jr.

So even assuming Mueller had to wait until talking to Kushner on April 11, 2018, he had the story on conspiracy nearly a year before releasing the Mueller report.