Why were confidentiality measures imposed in the first place?
In 1974 the California Supreme Court decision Pitchess v. Superior Court allowed a criminal defendant access to certain kinds of information in citizen complaints. Several law enforcement agencies “launched mass record-shredding campaigns to evade court orders pursuant to Pitchess,” resulting in the dismissal of criminal charges in those cities. After the state legislature required files to be maintained for five years, police unions pushed for confidentiality measures, and the result is the current restrictive law.