Why don't the German police just ask Facebook?
"A police probe turned up the MAC address f8:e0:79:af:57:eb, which, if genuine and non-spoofed, belongs to a Motorola/Lenovo device – most likely a Motorola smartphone."
Chances are high that if the user is running a stock ROM without ROOT that Zuckerbergs infamous Graph API is installed either by the Facebook app or any number of third party apps that use Facebook's API.
The Facebook Graph API scans and collects WIFI SSID , MAC address,etc.
private static final String PARAM_MAC_ADDRESS = "mac_address";
private static final String PARAM_LATITUDE = "latitude";
private static final String PARAM_LONGITUDE = "longitude";