innocent

[Ju]

Jo didn't say anything behind Paul but Paul and all people around are certain that Jo really did it.

1) Shall I say, "Jo is innocent in this issue."

2) Any better way to describe Jo's situation?

Thank you.

[Tdol]

behind Paul- behind Paul's back??

You could also say that Jo isn't to blame for this.

[JMurray]

Ju.
A few more ideas:
Jo has been unfairly/wrongly accused of this.
Everyone's pointing the finger but Jo's not at fault.
Jo's blameless in this, despite what they say.

not a teacher