There are many ways people find out dirt on others - it is usually through the grapevine. Unless what happened was in a vacuum and NO ONE YOU KNOW was aware of it, then someone told a friend, that person told a friend, and so on.
You will not get to file a lawsuit on a guess. It won't happen, and you won't be able to go fishing in an effort to try to find out why he knew the information. You have no proof that he accessed the information unlawfully in some way.
And, unlike the impression one might get from TV, it is simply not going to be the case that an officer in OR is going to have access to a local police report from an agency in CA. Unless, for some reason, the agency in OR needed the report and requested it from the CA agency, there is no way the OR officer would have known it existed much less sought the info.

