Google collects and retains location data from Android-enabled mobile devices when a Google account user has enabled Google location services. The company uses this information for location-based advertising and location-based search results. This information is derived from GPS data cell site/cell tower information, and Wi-Fi access points… It is probable that the unknown suspects of this investigation had cellular telephones which utilized either Google’s Android or Apple iOS operating systems.

Like all evidence, there is potential for issues when the collectors are not scrupulous.

1. Location services might be turned off. Really, if you don’t have a need, then it should be turned off. And, they tend to drain the battery, so turning it off would mean less frequent recharging.
2. Location services might not be precise. Several apps work on geofencing. The concept being that if a phone enters a certain location, then do something. As examples, I have something that will silence my phone when I get to work. Initially, I set it for not much wider than the building, but it often didn’t run. After a few iterations of expanding the area, it is now about a quarter mile wide and seems to be consistent now.
3. Device Identities. My wife let the stepson borrow her phone to play a game. He signed into Google on the Android device. While she signed back into her account, somehow she still got his Google Hangouts messages until she replaced the device. Google might report both of them being at the phone’s location if Hangouts provides location information.