Trace Evidence in Criminal Investigations

Use of Deoxyribonucleic acid (DNA) in crime investigations is an accurate way of determining who committed a crime as well as absolving suspects of crimes. DNA is found in all body cells with the exception of red cells and it is responsible for storage of an individual’s genetic information. It is unique to each person and this is what makes it accurate. However, great care should be taken to prevent contamination of DNA samples as this can give erroneous results thus there is a need for quality control.

DNA evidence collected at the scene of crime is usually profiled and matched against a database of DNA profiles known as Combined DNA Index System (CODIS) and this helps in identification of possible suspects (Federal Bureau of Investigation [FBI], 2010). Compared to traditional serology tests, DNA method has its advantages as well as its disadvantages.

One advantage is that unlike the serological tests which are limited to semen and blood samples, DNA can analyze a wide range of specimens e. g. hair and fingernail scrapings which cannot be analyzed by serology. DNA method is also specific in identifying the suspects since DNA is unique to individuals unlike serology which is not specific. For example serology can determine the blood group of a suspect but the problem is that many people share blood groups and thus can only be used to exclude suspects. It is also used to solve paternity disputes by analyzing the unique genetic composition of the child something that serological methods cannot do.

One of its disadvantages is that it is very expensive compared to serological tests. Another disadvantage is that it is very time consuming compared to serological methods. The third problem is that it is very sensitive and minor contaminations can give wrong results leading to wrong convictions. It also requires highly skilled staff compared to serological tests. Even with the advantages and accuracy of DNA analysis, there is the risk of problems arising during the analysis process which can make the results inaccurate and unreliable.

This led to the formation of a DNA Advisory Board that sets the standards to be followed to ensure quality of DNA results (FBI, 2010). One of the procedures is maintenance of a laboratory environment that minimizes contamination and this is usually by controlling access to the laboratory as well as by carrying out extraction and amplification in separate rooms (FBI, 2010). The second one is ensuring that the evidence is controlled and this is usually by ensuring that the samples are clearly labeled during the analytic period as well as ensuring safe storage of the evidence to prevent contamination.

Evidence control also includes retention of a portion of evidence sample in a manner that preserves its integrity in case queries arise in future (FBI, 2010). The third procedure is use of validated procedures and techniques. There should be written standard operating procedures (SOPs) in each DNA laboratory which are to be followed to ensure accuracy of results. These SOPs are usually prepared by a qualified laboratory manager (FBI, 2010). In addition to use of SOPs, the analytical procedures are monitored by use of standards and controls.

The fourth procedure is maintenance and calibration of equipments used. In each laboratory there should be written down programs which are to be used in calibration and maintenance (FBI, 2010). The fifth procedure is following written down procedures in recording the results obtained as well as procedures for releasing the DNA results and this is done to ensure that there is accurate information in case of future queries (FBI, 2010). The CODIS is operated by the FBI and it is made up of several indices.

These indices include missing persons, forensic, convicted offenders, unidentified human remains, and arrestees’ indices (FBI, 2010). Each state in U. S. creates its own database DNA profiles and later these profiles are uploaded to the national database. The convicted offender index contains the DNA profiles of all the people who have been convicted of crimes such as murder and rape. The DNA profiles of evidence found at the scene of crime are usually matched against the convicted offender indices and this helps to identify the suspect.

Each state has its own policies regarding to the crimes for which a convicted offender is required to submit their sample for DNA profiling (FBI, 2010). Forensic index comprises the profiles made from the DNA evidence collected at the scenes of crimes. This DNA profile is put in the computer and matched against other profiles in the forensic index and if matches are found, it means that the crimes are linked (FBI, 2010). These DNA profiles are then matched against profiles contained in convicted offender index to get suspects.

Missing person’s index contains DNA profiles of people who are missing. If the DNA profile of the missing person is not available, those of their close relatives are put in the database and it is usually matched against unidentified human remains to check if they belong to the missing individuals (FBI, 2010). When human remains are found but cannot be identified, the DNA profiles are usually entered into the unidentified human remains index and thereafter they are matched against Missing persons index for possible identification (FBI, 2010).

The arrestees index comprises of profiles of people who have been arrested and it is used like convicted offender index. Trace evidence refers to evidence that is found at the scene of crime in amounts that are small but quantifiable. Examples include hairs, fibers, soil, glass, and gunshot residue. For pieces of hair collected at the crime scene, on a victim, or on a suspect, the first step is usually to determine if they are of animal or human origin.

If the hairs are found to have originated from a human being, examinations are done to determine race, length, body area, disease, root type, and artificial treatment (FBI, 2010). In addition, the hairs are analyzed using mDNA technology and this helps to identify suspects (FBI, 2010). Fibers found at crime scene are examined to determine if they are artificial or natural. The fibers in question are then compared to fibers from a known source to determine if the fibers originated from that source after which the two fibers are linked.

The fibers are also compared to other fibers whose origin is unknown to link crime scenes. Gunshot residue is usually found on hands of someone who has fired a firearm, on the victim, or on the objects near the point of firing and it helps to determine who fired the gun and may give insight into the type of gun used (FBI, 2010). Traces of soil can be found on the victim or on the suspect. The traces of soil found on bodies of victims and those found on the crime scene are analyzed and used to link individuals to the crime scene. Glass as trace evidence can be found on bodies, vehicles, clothes, or at the scene of crime.

It can be found on the bodies of victims or suspects following cases such as hit and run as well as burglaries and can be used to link the suspected car or individual to a crime (FBI, 2010). It is clear that the DNA technique is a very useful tool in criminal investigations. However, there is need for strict implementation of quality control procedures to ensure that the results obtained are accurate. Reference Federal Bureau of Investigations (2010). Laboratory Services. Retrieved 2 May, 2010 from http://www. fbi. gov/hq/lab/labhome. htm