The FBI recently demanded from Google the data about all people using location services within a 100-acre area in Portland, Maine, as part of an investigation into a series of robberies. The request included the names, addresses, phone numbers, “session” times and duration, log-in IP addresses, email addresses, log files and payment information.
Police may have used location history is to see who has crossed paths of a person they were tracking. For example, suppose police are tracking an illicit drug distribution ring. Dealers meet with customers to deliver drugs.
In order to identify potential customers, police can see whose location data puts them in close proximity to the distributor they are tracking. Merely by being around a distributor, you then become a potential target of police operations.