Entrapped in the ice, he finds the sinners guilty of treacheries against those who with they had special relationships.
The above sentence is part of a high school lecture in a Canadian film I saw the other day, and I was quite surprised to notice this type of invertion of a relative pronoun around a preposition. Normally, I would expect to hear something like: "... against those with whom they had special relationships." or "... against those whom/who/that/- they had special relationships with."
The only thing I managed to find online was the following paper article: https://repository.upenn.edu/pwpl/vol23/iss1/32/ , which examines a similar type of inversion,—or 'swiping' as the writter calls it—, of a wh-word around a preposition, occurring in sluiced or coordinated wh-questions. It, however, makes no reference to relative clauses, which is my case.