Re: Has the forensic evidence ever been wrong?

Question: Has the forensic evidence ever been wrong?
Has there ever been a case were the evidence gathered by the forensic lab 
ever named the wrong person in a crime?


Dear Christine:

	The short answer to your question is, yes, improper evidence may 
have lead to false convictions of some individuals.  However, this is a 
difficult topic to research because mistakes made by forensic 
laboratories are generally not published in the professional journals.    
From the newspapers, one can read articles about how DNA analysis of 
evidence collected from a crime scene years age has exonerated a person 
sentenced to jail.  Generally speaking, convictions were made not based 
on forensic science, but on eyewitness accounts, perjured testimony etc.   

What is improper evidence?  Evidence that has been contaminated, evidence 
that does not have a proper “chain of Custody”.  Interpretation of some 
evidence may be subjective, that is, more that one type of conclusion may 
be reached from the same evidence.   For instance, in an article by Shor 
and Weisner (1), a survey of experts was conducted on footprint 
evidence.  Different conclusions were made and different reports were 
generated by several experts on the same foot print evidence. 

I would recommend your reading a book written by Peter W. Huber.  The name 
of the book is “Galileo’s Revenge - Junk Science in the Courtroom” (Basic 
Books,  New York.  The crux of this book reveals that Scientists are 
human beings and are subject to biases, errors, distractions and greed.  
The interpretation of evidence is not always based on good science.  This 
is a critical concept for you to understand.  Evidence does not speak for 
itself, someone has to gather the evidence, analyze the evidence, and 
interpret the results.

I would like to give you some background into the field of Forensic 
Science.  A Forensic Laboratory may be divided into may different 
departments according to function.  For instance, a Forensic laboratory 
may have a Chemistry or Toxicology section which would be responsible for 
the testing of  illicit drugs and chemicals.  The analysis performed in 
this lab may be on kilograms quantities of drugs (e.g. cocaine, marijuana 
etc.,) or on blood and urine samples taken from someone arrested for 
driving under the influence of a controlled substance.  The Serology section of 
a Forensic Laboratory would be involved with the identification and 
individualization of blood, sweat, and semen stains secured from crime scenes 
and / or victims  This type of testing usually involves the testing of DNA.  The 
Trace Evidence section will look at paint chips, glass fragments, fibers, tire 
and foot prints, fingerprints, hair and fibers.  Each of the above may link an 
individual to the scene of a crime.  The Arson laboratory would test the charred 
remains of a fire to determine if a flammable substance was used to start the 
fire.  Ballistics would look at bullets, firearms and gun powder residues.

Some types of evidence may find its way through one or more laboratories.  
For example, a hair may be identified as coming from one individual by 
light microscopy performed in the trace evidence section of a Forensic 
Laboratory.  This result could be confirmed by DNA Testing (only if the 
root of the hair is present!) performed by the Serology section. The hair 
could then be tested for drug content by the toxicology section.

Good Luck

References

1.)  Shor, Y & Weisner, S: A Survey on the Conclusions Drawn on the Same 
Footwear  Marks Obtained in Actual Cases by Several Experts throughout the 
World.  Journal of Forensic Science, 44(2)  pages 380-384, March 1999