The Good Hart Murders

In 1968 in Good Hart, Michigan, the Robison family was on a vacation in a remote cabin on Lake Michigan.  Even though they weren't discovered for over three weeks, and even though there was plenty of evidence to charge a person of interest with the murders, it was nearly five years before a new prosecuting attorney would do so. 

Sources for this episode:
Wikipedia - Readmond Township, Michigan
Wikipedia - Robison family murders
Northern Express - Good Hart Murders: Case Closed
9 and 10 News - Unsolved: The Robison Family Murders
MLive - 50 years after Michigan family's massacre in cottage, investigators put rumors to rest