Forensic DNA Analysis

In the early 1950s scientists were racing to try and discover the structure of DNA. They were pretty sure it was genetic material but no one understood how it worked or how it could determine things like a person's eye or hair color, height, skin pigmentation, etc. Although dozens of the world's top scientists were studying DNA, none of them had any idea that fifty years later DNA would become a critical piece of evidence in criminal prosecution cases from thefts, rapes, and child abuse to abductions and even murders.

In the law enforcement world of 2007 DNA has become the cornerstone of a large number of criminal cases. DNA analysis is a very sensitive process that must be performed under strictly controlled and documented conditions if the results are to withstand the scrutiny of the defense in a trial. Unfortunately, the TV world has led the public, and in particular the potential members of juries, to assume that DNA results should be indisputable and immediately available. However, the time needed to obtain DNA analysis data is often much longer than investigators and prosecutors would like.

The Backlog Problem

If you lived in the television CSI world of Miami or Las Vegas, you could order DNA analysis on three samples taken from a victim, and cheek swabs from four potential suspects and then get your definitive results back before you could go out, eat a pizza for lunch, and return to your desk. Unfortunately, most of us have to deal in the real world where things cannot be accomplished in 60 minutes. Police forensic labs performing DNA analysis must work within the time constraints of the analytical technology. Extended sample preparation time, the need for repeat analysis for confirmation, and the laboratory backlog of samples is among the many reasons for the extended time period needed to obtain accurate DNA data.

While all these factors add to the timeline for analysis, probably the most important factor is laboratory backlog. Setting up a DNA laboratory and training technicians to run the required assays accurately is not an easy task. The cost of the necessary equipment is also quite high. This makes it difficult for smaller police department to set up their own lab and therefore must rely on state police crime labs or outside, commercial labs to perform their analysis. Backlogs at these labs have resulted in turnaround times of six months or more.

A laboratory backlog occurs when a lab simply has too many samples to analyze per day or week with the trained technicians and laboratory equipment available. If the backlog in a lab is approximately 100 samples and the rate of new samples received is a constant 100 per week, then at the end of a month the backlog is 400 samples; at the end of six months it is 2400 samples. This assumes an ideal situation where technician do not get sick or go on vacation, equipment does not break down and prosecutors do not add high profile samples (which must be analyzed right away) into the middle of the queue. If money were no object then labs could simply buy more instruments, train more technicians, work 24/7, and solve the backlog problem.

Solving the Backlog Problem—

If life was this simple then the solution above would work. However, things don't work that way. As DNA evidence has become more and more critical to convictions in all sorts of cases, the number of samples being submitted for analysis has grown exponentially. The number of independent commercial laboratories performing DNA analysis (150 labs) has grown over the last ten years as has the number of law enforcement laboratories (over 30 State labs). However, this growth has not been able to keep up with the growth in samples. Congress realized the need for added lab capacity and passed The DNA Analysis Backlog Elimination Act of 2000 which sought to identify the need and provide a means for federal funding (budget of $170 million over four years) in an attempt to meet this need.

However, while federal money can provide dollars to buy equipment, train technicians and build laboratories, it is not the total answer to solving the problem. As forensic DNA analysis science matured there also developed a need for standardized testing protocols, control samples, quality control practices and measurements to ensure that analysis of forensic DNA analysis was reliable in all jurisdictions. This is critical because the outcome of a DNA analysis may determine whether a suspect lives or dies, or spends the rest of their life in prison.

A primary goal for all laboratories has been to decrease their turnaround time for sample analysis. Turnaround time (TAT) is defined as the amount of time required from the time of sample receipt at the laboratory to the time a final report is provided to the requesting department. TAT will vary from lab to lab and also from sample to sample. Labs which are highly automated with robotic analysis equipment can process samples faster than those using manual methods. Different types of analysis require different times to perform. Often test results are inconclusive and must be repeated to more provide a definitive answer. Repeat testing not only adds to the time required to get the results for the test sample in question, but also to the overall backlog of the lab. As an example of how sample load affects TAT, take for example a simple cheek swab taken from a suspect. Two independent samples are taken from the suspect. One sample is placed in an archive storage as a "backup sample." The other sample is extracted In the lab and then, at a minimum, each sample is analyzed in duplicate. So the sample from a single suspect actually produces two analyses. It you have 10 individuals that must be screened, the analysis load quickly rises to 20. Since each lab has a fixed capacity to analyze samples, it is obvious how the backlog is created.

New Technology and Analysis Methods

The introduction of newer analytical technology has led to faster and more definitive analysis. The introduction of the Short Tandem Repeat (STR) test procedure has allowed for more reliable analysis on samples which previously were too small or too degraded to analyze. The CODIS database works on the recognition of 13 specific STR loci. The development of highly automated equipment to facilitate handling of large number of samples has greatly increased the number of samples that can be analyzed. Many larger labs have gone to automated robotic equipment that handles many of the manual operations that technicians routinely performed in the past.

The introduction of fluorescent tags, gas chromatography and now mass spectroscopy equipment to the DNA analysis arsenal has added a new dimension to forensic DNA analysis. However, due to the sizable cost of this equipment, only large labs like the FBI, major commercial laboratories,sState and some major large city labs will be able to have this type analysis available. Small departments will not be able to develop these methods because they cannot afford the costly equipment, nor will they be able to afford the technicians to run them. Thus, the backlog issue, while improving, will be with us for a long time.