One case saved a man from the electric chair and another put an end to a sniper's murderous rampage. Revisit two criminal cases where ballistic evidence played a key role in determining the fate of its suspects. First, Charles Stielow, a man sentenced to death for a 1915 murder, is absolved thanks to a pioneering investigation. Then, after a harrowing 22-day span in 2002, detectives in Washington D.C. finally crack the case of a sniper, relying on bullets taken from the victims' bodies.

• Denny Heide