St. Valentine's Day Massacre - HISTORY DETECTIVES stares down the barrel of a shotgun for clues that one of Al Capone's men fired it in a Chicago gang massacre that shocked the nation. The gun came to the contributor's family after it was handed down through two generations of prominent Chicago families. It's a Western Field single-barreled repeating action 12-guage shotgun. The barrel and the stock were once shortened just the way the Capone gang liked its guns: easy to conceal and with greater destructive force. HISTORY DETECTIVES host Elyse Luray tests the gun's firepower, consults with ballistics experts and combs through physical evidence to see if she can place this gun at the scene of the crime. Booth Letter - A contributor gave HISTORY DETECTIVES a letter indicating that, 30 years before John Wilkes Booth assassinated Abraham Lincoln, Booth's father threatened to kill another sitting president, Andrew Jackson. Signed "Junius Brutus Booth," the letter to Jackson reads, "You damn'd old scoundrel ... I will cut your throat whilst you are sleeping." The writer insists that Jackson pardon two men who were sentenced to death. Why did the fate of these two men incite such fury? HISTORY DETECTIVES host Tukufu Zuberi travels to Nashville to consult historians at The Hermitage, the ancestral home of President Andrew Jackson, and to Washington, DC, to talk with a Booth biographer. Was the letter a hoax? Or did assassination run in the Booth blood? Cemetery Alarm - A Midland, Michigan, man who collects war munitions snapped up an item at an estate auction that looked like a Civil War-era weapon. On closer inspection, after consulting with other collectors, he decided he had a grave alarm: an explosive device meant to guard against grave robbers. Is this truly a grave alarm? HISTORY DETECTIVES host Wes Cowan's investigation winds through tales of body snatching and cadaver dissecting, unusual crimes and the most unlikely suspects.