Forensic evidence is a key element in gaining a conviction in most criminal cases. Sometimes the evidence is clear cut as in the presence of fingerprints, DNA or blood evidence of a perpetrator being at the scene or found on a victim. In many cases the evidence is circumstantial trace evidence like hair or fibers or paint fragments. If sufficient circumstantial evidence is present then it is possible to build a definitive case against a specific suspect. However, forensic evidence can become a "Catch 22" and it is important for law enforcement officers to understand the limitations of forensic science.
Advancing Technology - The rapid advancements in science and technology over the last two decades have led to an explosion of new techniques and equipment which are being applied to forensic analysis. Most of these procedures have been developed in university research laboratories and while the science behind their development is sound they have not had extensive field testing and verification in real world forensic laboratories. In addition, the methods for performing these procedures have not been standardized so there is the potential for variable results between different crime laboratories for the same evidence sample.
Fingerprint analysis has been a keystone of forensic analysis for more than a century. Certification programs exist to ensure that fingerprint analysts are perform their analysis accurately and according to standardized procedures. The AFIS and IAFIS systems allow print matching to national database in a standardized procedure that minimizes analyst’s errors. New techniques to enhance and further identify latent prints have been developed. These include the superglue fuming procedure, use of colored powders to enhance the print and Alternative Light Sources (ALS) to help visualize print at the crime scene or on a piece of evidence.
DNA has taken center stage in recent years as the evidence of choice in cases where DNA evidence can be obtained. Unfortunately TV programs like the many CSI variants have led the general public that makes up juries to expect definitive DNA analysis in every case. While the methods for DNA analysis is scientifically proven and sound there is again the potential for variability between laboratories. Standard Accreditation programs like ISO 17025 and Forensic Requirements for Accreditation (FRA) have gone along way to ensure accuracy in this field but variability still exists. Problems in sample collection and storage as well as contamination can complicate DNA analysis and interpretation.
Reevaluating Old Cases -The reinvestigation of old rape and murder cases by analyzing DNA evidence has established the innocence of over 200 individuals who were convicted of the crime before DNA analysis became available. Many of those individuals, like Kennedy Brewer, have served long jail sentences for crimes they did not commit. Brewer had spent twelve years in various Mississippi Jail and prisons, including time on death row, for the rape of a three year old girl that he did not commit. Recently Justin Johnson was arrested for commission of that crime.
Expert Testimony - Brewer and others like him were convicted on circumstantial evidence or in many cases presented by an expert in the field whose credentials have subsequently been called into question. In Kennedy Brewer's case the conviction was largely based on the testimony of a local expert that the bite marks on the victim’s body matched Brewer's dental pattern. Reinvestigation of that evidence by other experts in forensic odentology indicate that the bites marks were from animals and were made on the body after it was dead and disposed of.
All areas of forensic analysis require well trained and qualified analysts. However, some areas require more training and certification than others. It is important for law enforcement and prosecutor to recognize the limitation of their local crime lab when evaluating critical pieces of evidence. Likewise, the credentials of experts brought in to assist in evidence analysis must be closely scrutinized. How much experience does the individual actually have in analyzing real world forensic evidence, what certification in the area of expertise do they have and do they periodically get recertified all are questions that need to be considered.
Two areas where special training and certification are particularly essential are in bloodstain spatter analysis and forensic audio/video analysis. Recent advance in computer software, digital cameras and laptops computers have all greatly increased the ability to collect data in these areas. However, the analysis of the data obtained still need the care of a well trained and experienced analyst to ask the right questions of the data and understand any specific nuances in a particular case. While these and other areas of forensic analysis have certification programs specific to their area it is important for law enforcement to understand that not all certification programs are equal. The American Bar Association has asserted that certain certification agencies are merely certification mills in which certifications are many times simply bought and sold.
Dilemma for Small Departments - Small and even mid-sized departments usually cannot afford to have a cadre of experts on staff and therefore must rely on outside experts. An expert's experience far outweighs a certification document that they may have. Proper formal education and training, hands-on training and mentoring with a qualified senior examiner are the criteria that should be most important in evaluating potential expert candidates.
It is important for investigators to understand that circumstantial evidence can never directly indicate that a suspect is guilty. At best, it can provide a piece of the much bigger puzzle of evidence needed to convict a specific suspect. In the past all too often a jury has been convinced of a suspect's guilt based on a few fibers or hairs found at a crime scene. Microscopic analysis of hair and fiber can provide a presumptive match to a perpetrator but can not establish that it is definitely their hair or fibers from their clothing. The exception, of course, is if the hair has a root attached upon which a DNA analysis can be performed. Advanced microscopy methods like the use of scanning electron microscopy (SEM) are providing better visualization of trace evidence but again the training and experience of the analyst is essential in obtaining reliable, defensible results. In addition, SEM and other analytical tools recently introduced in to the forensic laboratory cost anywhere in the range of from tens-of-thousands to hundreds-of-thousands of dollars a cost most laboratories can not bear.
FBI Evaluating Old Methods - As a final example of how forensic analysis has changed in recent years in September of 2005 the FBI Laboratory officially announced the "Discontinuation of Bullet Lead Examinations" procedures as evidence acceptable for use in trial. Bullet lead analysis has been a mainstay of forensic analysis for decades and has been one of the determining factors in a jury's decision to find a suspect guilty in murder cases. This decision was based of research that demonstrated that bullet lead composition was not constant throughout preparation of a batch and that it could actually vary considerable between bullets produced at the beginning and the end of a production batch.
We must view all forensic evidence as supportive information and not allow a case to be built solely on its merits. Even our current love affair with DNA must be viewed in this regard for there are many factors and issues that can cloud DNA analysis results. Defense attorneys are becoming much better versed in the vagaries of DNA analysis.
