Historically, from the time God questioned Cain in the death of Abel, the first recorded homicide, society has sought a more definitive way to test the veracity of their fellow man.  Trial and error, observations and carefully listening to victims, witnesses and suspects produced a variety of answers to this age old problem.  

IN ANCIENT CHINA

The ancient Chinese reportedly belived that stress limited the salivary glands' ability to produce saliva, causing the 'guilty' to have a dry mouth.  The accused was required to chew rice and spit out a ball to prove their innocence.  However, under stress, the "guilty" could not produce the saliva necessary and were unable to produce the ball of rice, but instead spit out kernels.  Unfortunately, for the nervous but innocent suspects, their fate was uncertain.

THE DARK TENT

Recorded history tells of the subterfuge where a donkey was placed inside a dark tent.  The suspect was to enter the tent alone and pull the donkey's tail. If the donkey brayed, the suspect was told they would be presumed guilty.  The theory was that the guilty would not pull the donkey's tail, not knowing that coal soot was on the donkey's tail and with they emerged from the tent with a clean hand; they were immediately pronounced guilty.

BODY LANGUAGE

Not restricted, astute observers noted that guilty persons more often than not displayed a certain 'language' or 'signs' that could be associated with guilt; a darting eye, dry mouth, a hand over their mouth when answering, sweating, yawning and uncontrolled body movements during interrogations. Again, this method as stand-alone was less than scientific; failing to take into account even innocent suspects may demonstrate the same body language due to a fear of egregious consequences.

THE POLYGRAPH

These observations were followed by years of experimentation with instruments designed to record changes in the body during interrogations. The polygraph was the first instrument designed to record these reactions associating stress with the guilty. While extremely useful, documenting much success by law enforcement and military, failures were equally noted.

VOICE STRESS ANALYSIS

Today voice stress analyzers, after a lengthy learning curve, are enjoying an increased popularity among law enforcement professionals due to their relative non-invasiveness.  Voice Stress Analyzers, used in concert with low stress interview techniques (rather than interrogations) have bridged the gap from the out-dated hot lights and aggressive interrogators coerced confessions.