In Greg Bear's novel "Queen of Angels", set in 2047, their solution to the conflicting needs of privacy and crime prevention was a separate organization called "Citizen Oversight". All the digital-trail data (cameras, financial records, etc) flowed into Citizen Oversight. If law enforcement wanted data, they had to ask for it and demonstrate need on a case-by-case basis. In that world it wasn't a perfect solution; if I recall rightly, part of the novel is driven by Citizen Oversight's swing from a too-loose era to a very stingy one. But I liked the idea of there being specific, named people responsible for protecting privacy.