The prisoner’s dilemma

In a seaside village in Brazil, four high class friends on vacation run over and kill a child. They are taken to the Police Station, where the Police Chief interrogates them to find out who was driving before the Army arrives to take them to the capital. Enraged villagers pressure outside to take the law into their own hands, knowing that the Army will leave them free. The Police Chief interrogates them separately, but they have done a pact of silence, if they don’t betray the culprit, nobody will be punished (this is the prisoner's dilemma stated by JF Nash). The commissioner must find out what happened in recent days and the reasons for each to be silent, but the Police Chief also has an ulterior motive to get the case solved.