Identification Problems in Forensics

Forensic identification refers to the use of scientific methods to individualize trace evidence--that is, to tie a particular scratch, bullet hole or drop of blood back to one specific knife, gun or person. Forensic identification can also refer to determining the identity of a corpse. Problems in forensic identification include logistical issues of statistical analysis, errors in sampling or evidence collection, and lack of baseline identification records regarding identification of unknown deceased persons in natural disasters and war.

New forensic identificaton techniques are not always as clear as fingerprints.

Types

Criminal forensic identification involves matching trace human evidence at a crime scene--fingerprints, hair samples, blood, saliva--to a particular person. Tool mark forensic identification means matching the mark made by a specific hammer or knife or crowbar to scratches, dents or wounds. Ballistic forensic identification is the science of determining whether a bullet was fired by a particular gun. Anthropological forensic identification means seeking the information about a dead person, from identifying individuals recently killed in war, disasters or accidents, to learning about the culture and cause of death of exhumed archaeological remains.

Significance

Most forensic identification evidence is prepared relative to criminal cases, particularly in regards to tying the defendant to a crime scene. Criminal forensic identification evidence is significant, in that it is frequently the only evidence on which a decision is made to send a person to jail for life, or even to the execution chamber. Anthropological forensic identification is also significant, in that through application of dental records, fingerprint and DNA testing and other methods, scientists can help notify loved ones accurately of the fate of their family members.

Misconceptions

Two dominant misconceptions regarding forensic identification are first, that identifications made are absolutely certain, and secondly, that forensic identification tying an individual to a crime scene equates to guilt. The first problem of forensic identification is that individualization is never certain, it is a matter of probability. Those probabilities vary depending on the nature of the identification and the level of detail of the trace evidence being used for identification. The second problem is that a fingerprint on a bank counter demonstrates that a particular person was present at that location, but does not prove that they robbed the bank. Despite the assertions made by popular television crime detective shows, forensic evidence alone can rarely prove actual guilt.

Identification

Anthropological forensic identification of large numbers of corpses in circumstances of war, accident or natural disaster can be problematic in areas where there were not base records available for comparison or where those records were also destroyed. Corpses are often identified by evaluation of dental records, fingerprints or DNA samples, but in more impoverished or war-torn areas of the world, medical records may not exist for the victims, and extended family may be displaced, making the means of identification extremely difficult.

Considerations

Criminal forensic identification begins with careful analysis of trace evidence left at a crime scene. Identification problems can start with errors in gathering that evidence. Crime scene investigators must give careful consideration to how to collect evidence for forensic identification testing. For tool mark analysis, photographs may be adequate in some instances, but in most cases forensic laboratories will want the actual artifact to be cut out of the wall or floor in a manner which does not destroy it. Blood, hair, saliva and other DNA evidence must be collected with great care to avoid contamination.

Size

Problems in forensic identification can arise if evidence samples are too small to run adequate testing. Problems also develop when the sample set is too small to create an appropriate analysis of statistical probability regarding the odds of, for example, whether a mark was made by a particularly unusual tool or weapon. DNA analysis depends heavily on comparison of known results to databases reflecting the demographics of population in the area. When that database is large and its ethnic and racial components change rapidly, problems may also arise in establishing accurate probability predictions associated with identification.

References

• , Champion Magazine NACDL; Evaluating and Challenging Forensic Identification Evidence; Tobin and Thompson
• KQED Education Network; Forensic Identification
• International Association for Identification

Resources

• Forensic Identification Science; Saks, Arizona State U. College of Law