Two masked robbers try to rob a crowded bank during the lunch hour, but the teller presses a button that sets off an alarm and locks the front door. The robbers, realizing they are trapped, throw away

Two masked robbers try to rob a crowded bank during the lunch hour, but the teller presses a button that sets off an alarm and locks the front door. The robbers, realizing they are trapped, throw away their masks and disappear into the chaotic crowd. Confronted with 40 people claiming they are not guilty, the police give everyone a lie detector test. Suppose that guilty people are detected with probability 0.85 and not guilty people appear to be guilty(a false positive) with probability of 0.08. What is the probability that Mr. Smith, the first person to be given the test, was one of the robbers given that the lie detector says he is guilty? Is this a good test?