Lol! But to be fair, that's not what he said.
"And as set forth in the report, after that investigation, if we had had confidence that the president clearly did not commit a crime, we would have said so. We did not, however, make a determination as to whether the president did commit a crime."
Which in simplified English is
Based on the evidence we have collected, we cannot say definitely that the president did not commit a crime, but we also cannot say he did. (Because as stated earlier it would be illegal for them to accuse or arrest a sitting president under congressional rules)
So in short Muller say "I Cannot act on these findings, but you can!"