MacGyver: Slow Death

MacGyver has to jump onto a moving train that he missed earlier to return top-secret files and documents to the US government. Soon after, a local tribe stops the train. They take all passengers hostage until the men responsible for the death of the tribal leader's son is found among the passengers. MacGyver, after learning the reasons for the hijacking, agrees to help the men find who they are looking for. He constructs a lie detector and sets about trying to find the guilty party. But who is guilty?