... Mueller does not declare people innocent. People are assumed innocent in our country. So Mueller cannot exonerated because that implies a person as being guilty beforehand. ....
BBc:
Mr Mueller said he had not exonerated Mr Trump of
obstruction of justice.
The Justice department works independently from the political arena. That is the ideal situation and a fundament of the how the country ( and mine) operates.
The problem arises when these areas meet, as in this case.
Trump has tried to fire mr Mueller-( a republican BTW) - That is an attempt to interfere with the justice system.
That is serious. Certainly in the light of the conclusion that Russia interfered with the election to benefit Trump.
Also Trump did not fully cooporate with the investigation of Mueller.
(Mr Mueller said that the special counsel's office repeatedly requested an interview with the president but was refused, eventually securing some written answers from the president.)