A line of inquiry has to be ruled in or out ? As Mr Spock once said in Star Trek - " If you eliminate the impossible, whatever remains, however improbable, must be the truth."
The mobile phone masts collect data , if the phone is switched off it will still be picked up by cellular towers as you pass through and the signal triangulated to pinpoint an exact location.
You can be tracked everywhere you go these days , the SIM card in your mobile leaves a "footprint" even when the phone is switched off. Once your movements have been established you're bound to show up on CCTV footage matching the timeline.