A Signal 51 is police code for an investigation, a law enforcement proceeding that is a systemic and thorough attempt to learn the facts about a possible crime that is complex and whose facts and circumstances are generally hidden, at least initially, behind obstacles that can be circumstantial or manmade. The investigation’s methods are formal. John Henry, a journalist, and retired Fort Worth police sergeant Jake White examine the difficult cases of law enforcement both in Fort Worth and around the region.