I saw this documentary...
It was called "The Sweeney", set in London. Apparently policemen in plain clothes used to arrest criminals in the act of doing crimes at locations such as airports, warehouses and banks. But noone had mobile phones.
Could we please ask the creators of this practical guide to policing for their help? It would seem that before there were mobile phones that could be tracked, criminals were still caught in the act of doing bad stuff.
Planet Gliese 51C, constellaion Libra