When Barr referred to the fact that he didn’t have answers to his questions he probably referred to misconduct of Mueller and Rosenstein. Rosenstein didn’t have justification and mandate to expand the probe of the OSC to begin with. The extended mandate let to the Obstruction fishing expedition and to the extension of the probe which influenced the 2018 midterms results. He should have asked for the extension in congress which he didn’t. Rosenstein recommendation of Sessions to recuse was unfunded and put him in a position where he could carry out Comey and McCabe political agenda.

” I had a lot of questions about what was going on. I assumed I’d get answers when I went in and I have not gotten answers that are well satisfactory, and in fact probably have more questions, and that some of the facts that, that I’ve learned don’t hang together with the official explanations of what happened.”

https://thefederalist.com/2019/06/03/top-28-moments-from-bombshell-barr-interview/

Mueller was asked if “Was the purpose of the investigation to find a crime vs. investigate a crime?”

The unanswered questions indicate that the purpose of the probe was to smear the president and fabricate a crime for political reasons and cover up instead of pursuing justice.