Your three sentences have no connection. Please start new separate threads for the sentences about the locked building and about slavery.
With regard to your first sentence, none of your three examples work in BrE. We don't get a "clean chit" in any context that I'm aware of. If you're accused of a crime but the police do not gather enough evidence to charge you with that crime, they have to simply let you go. If you are charged with the crime but then you are found not guilty at trial, then you would say that you had been found "not guilty" or maybe that you had been "exonerated/cleared" at trial.
If you're arrested for something, but later cleared, you might be able to bring a case of "wrongful arrest" against the police.
Student or Learner