But decades earlier the Stasi had their own methods to secretly mark people: radiation. They had radioactive magnets for cars, put radioactive pins into clothes, and had radioactive pellets shot into tires. A radioactive spray could be surreptitiously used on anyone in a crowd, and if used on a floor it could make a target unknowingly leave radioactive footprints wherever they went. These techniques were only later put together because several prisoners all died from an unusual form of cancer, which led to investigators discovering a radiation machine.[cdxxvii]
