At the time Mueller’s letter was sent to Barr on March 27, Barr had days prior announced that Mueller did not find a conspiracy between the Trump campaign and Russian officials seeking to interfere in the 2016 presidential election. In his memo to Congress, Barr also said Mueller had not reached a conclusion about whether Trump had tried to obstruct justice, but that Barr reviewed the evidence and found it insufficient to support such a charge.

Days after Barr’s announcement, Mueller wrote the previously undisclosed private letter to the Justice Department, laying out his concerns in stark terms that shocked senior Justice Department officials, according to people familiar with the discussions.

“The summary letter the Department sent to Congress and released to the public late in the afternoon of March 24 did not fully capture the context, nature, and substance of this office’s work and conclusions,” Mueller wrote. “There is now public confusion about critical aspects of the results of our investigation. This threatens to undermine a central purpose for which the Department appointed the Special Counsel: to assure full public confidence in the outcome of the investigations.”