This program raises again and again the question of whether Lightman is infallible. Does he make mistaken judgments about whether someone is lying or guilty of a crime? Those are not the same. Not everyone suspected of committing or planning a crime tells the truth about everything. Most people have something to hide. And once an innocent person knows he or she is suspected of a crime, the suspect may conceal and falsify about some matters. Sometimes it is past actions that if known might put the suspect in a bad light, increasing the chances that the police will think they have the right person. Sometimes the lie is to cover up some other misdeed – the person who was in bed with his wife’s sister at the time the crime was committed is not likely to truthfully acknowledge it, but falsely claim to have been somewhere else. Anger about being under suspicion, fear of being disbelieved, excitement at the challenge of outwitting the cops, are some of the emotions an innocent suspect may feel but try to conceal.