NCJ Number
63145
Journal
Australian Journal of Forensic Sciences Volume: 10 Issue: NOS 3 AND 4 Dated: (MARCH-JUNE 1978) Pages: 93-110
Date Published
1978
Length
18 pages
Annotation
THE USE OF PROBABILITY CALCULATIONS IN DETERMINING THE IDENTIFICATION OF A SUSPECT IS EXPLORED THROUGH DISCUSSION OF NUMEROUS HYPOTHETICAL EXAMPLES OF PERMUTATIONS OF A GIVEN SET OF FACTS.
Abstract
IDENTIFICATION IS OF TWO KINDS. THE FIRST INVOLVES RECOGNITION, AS WHEN A WITNESS LOOKS AT THE ACCUSED AND IDENTIFIES HIM AS THE PERSON WHO COMMITTED THE CRIME. SOMETIMES THE ACCUSED IS ALREADY KNOWN TO THE WITNESS; OFTEN HE IS FIRST IDENTIFIED THROUGH POLICE PHOTOGRAPHS OR A LINEUP. IN THE SECOND TYPE OF IDENTIFICATION CASE, THE PROSECUTION SEEKS TO IDENTIFY THE ACCUSED, NOT BY EYE WITNESS RECOGNITION, BUT BY ESTABLISHING THAT THE ACCUSED POSSESSES CERTAIN CHARACTERISTICS WHICH ARE ALSO POSSESSED BY THE CRIMINAL. IN THE SECOND TYPE, THE FOCUS OF THE DISCUSSION HEREIN, THE QUESTION IS REALLY ONE OF PROBABILITY, AND DEPENDS ON THE COMBINATION OF CHARACTERISTICS BEING SUFFICIENTLY UNUSUAL TO ENABLE THE TRIBUNAL TO SAY THAT THE DEGREE OF PROBABILITY OF IDENTITY IS HIGH ENOUGH TO SATISFY THE REQUISITE STANDARD OF PROOF IN THE CASE. THE CASE OF THE 'PEOPLE V. COLLINS' ILLUSTRATES THIS CONCEPT WELL. MALCOLM COLLINS WAS A BLACK; HIS WIFE JANET WAS A WHITE WOMAN WITH BLOND HAIR TIED IN A PONY TAIL. MALCOLM DROVE A YELLOW CAR. A ROBBERY WAS REPORTED TO THE POLICE, ALLEGED TO HAVE BEEN COMMITTED BY A BLOND WITH A PONY TAIL, WHO WAS DRIVEN IN A YELLOW CAR BY A BLACK MAN WITH A MOUSTACHE AND BEARD. MALCOLM HAD WORN A BEARD AND MOUSTACHE AT ONE TIME BUT THE EVIDENCE AS TO WHETHER HE HAD SHAVED BEFORE OR AFTER THE ROBBERY WAS CONFLICTING. THE DAY AFTER THE ROBBERY, MALCOLM HAD PAID TRAFFIC FINES TOTALING ABOUT THE SAME AMOUNT AS THE MONEY STOLEN. AT THE TRIAL, THE PROSECUTOR CALLED A MATHEMATICS INSTRUCTOR WHO GAVE EVIDENCE ABOUT THE MULTIPLICATION RULE AND PROBABILITY CALCULATION. THE FREQUENCY OF OCCURRENCE OF SUCH FACTORS AS A YELLOW CAR, A GIRL WITH BLOND HAIR, A GIRL WITH A PONY TAIL, A BLACK MAN WITH A BEARD, AND AN INTERRACIAL COUPLE IN THE CAR WAS DETERMINED. USING THESE FIGURES, I.E., THE CHANCE OF AN INTERRACIAL COUPLE BEING IN THE CAR WAS 1 IN 1,000, THE PROSECUTOR ARGUED THAT THE CHANCES OF MALCOLM AND JANET NOT BEING THE GUILTY COUPLE WERE ONLY 1 IN 12 MILLION. THE CASE IS FAMOUS BECAUSE THE COMBINATIONS OF CONDITIONAL PROBABILITIES WERE NOT CALCULATED CORRECTLY. IN ANY PROBLEM OF IDENTIFICATION, FACTORS IN ADDITION TO CHARACTERISTICS WHICH MUST BE CONSIDERED INCLUDE THE SIZE OF THE POPULATION OF INTEREST, THE FREQUENCY WITH WHICH THE CHARACTERISTICS OCCUR IN THE POPULATION, AND THE POSSIBLE SUSPECT-SELECTION TECHNIQUE. REFERENCES AND MATHEMATICAL FORMULAS ARE INCLUDED IN THE ARTICLE. (LWM)