Not long ago a border patrol agent was moonlighting as a serial prostitute murder, he got past the polygraph too. I know people who passed their polygraph despite having done some really messed up stuff in the past like drug dealing and I know other guys who are choirboys and the person running their polygraph accused them of being murderers, drug dealers and pedophiles. The problem is twofold, polygraphs don’t work and the people administering them are incompetent and often biased.