The Butler County Sheriff's Office, without examining any of Miller's electronic devices, concluded they didn't have probable cause to bring criminal charges

That's a rookie mistake by the cops right there.

If the simple claim that his ex-wife stated about him sending her paedophilia images was true then there should be evidence of it.

That's where they can start to build a case from.

As for the board not firing him there is the possibility that he's being stitched up by the ex-wife which would be an ethical violation to take action from.

One illegal image sent from his phone to hers was all that was needed.