At the turn of the Twentieth Century, many in the fields of criminology and law enforcement believed that criminals could be tracked by carefully mapping the shape of their skulls. This discipline, called phrenology, was supposed to revolutionize the science of criminology.
Except phrenology was thoroughly discredited as a method of understanding criminal behavior, and is now considered no more scientific than astrology.
In the 21st Century, we have "ballistic fingerprinting", which is supposed to leave a unique identifier on each bullet casing that can link it to the gun from which is was fired. Like phrenolgy, ballistic fingerprinting is junk science. Yet the media and gun control groups are clamoring for it as the way to prevent more sniper shootings. As Satayana once astutely noted, those who fail to learn from history are doomed to repeat it, and ballistic fingerprinting will be as effective against crime in this century as phrenology was in the last.