How Long Do Forensic DNA Results Take?

by | Nov 22, 2019

I’m sure you’ve heard in the news about DNA backlogs at crime labs throughout the country. Agencies send in their evidence, and it can take months or even years to get the results back. How can DNA results possibly take that long? Should you use real-world turnaround times when writing your books? Or make one up?

Most public crime labs do have a backlog, which happens when more cases came in than went out in a given time frame. Many factors can affect how long a DNA case takes. In my 7-year career as a forensic scientist, the turnaround time for cases in the DNA section fluctuated from 14 months (when I first started) to 2 months (about halfway through my time there) to 6 to 8 months (when I left). The decrease in turnaround time was the result of a new technology/workflow and two additional forensic scientist positions. It increased because of an influx in submissions and staff turnover.

In this post, I explain the different factors that can affect turnaround time, why some cases take longer than others, and a reasonable amount of time for you to use for getting DNA results back when you’re writing your books. But first, a quick summary of how forensic DNA analysis works is necessary.

Overview of DNA Analysis in a Crime Lab

1. Screening

A forensic DNA analyst first looks for body fluids and other biological materials. If the case is positive, representative samples are selected for DNA testing. If the case is negative, a report is written and technically reviewed, and the evidence is sent back to the agency.

2. DNA Analysis

Samples selected for DNA testing are taken through a very specific workflow that includes getting the DNA out of the cells, figuring out how much DNA is present, making copies so there’s enough DNA to work with, and running the amplified DNA on an instrument called a genetic analyzer to get the DNA profile.

3. Data Interpretation

The DNA profiles from all the samples in a case are analyzed by a software program and interpreted by the DNA analyst. The analyst then compares the profiles and makes conclusions.

4. Report Writing

Once the conclusions are made, the DNA analyst writes a report on his or her findings, which is released to the submitting agency after technical review.

5. Technical Review

In forensic DNA casework, all reports must be technically reviewed by another qualified DNA analyst. The reviewer goes through the case file and reviews the findings and conclusions for technical accuracy. Once the reviewer signs off on the report, the evidence is released back to the agency and the report is sent out.

How long it takes a case to go through this process can vary. The exact workflow can differ from lab to lab, but DNA cases are typically taken through the above process in batches (which is more efficient).

One factor affecting turnaround time is the size of the case (i.e., number of items submitted for analysis). A complicated homicide or assault case with dozens of items and multiple suspects and victims will take a lot longer than a simple burglary with a few items.

Another factor is the type of case. The screening process for sexual assaults takes longer because the tests used to screen for the presence of semen are more time consuming. The DNA portion of the workflow can also take longer because getting the DNA out of sperm cells requires a special (longer) procedure.

In addition, after analyzing the data, the analyst may decide to go back and take another round of samples through the workflow or re-run samples. There are several reasons why a DNA analyst would do this:

  • In a larger case, the analyst may go back and choose a different set of stains to ensure a representative sample was analyzed.
  • Unexpected results can also be a reason for re-analysis. I once worked a homicide case where I took cuttings from a bloodstain on a pair of jeans. When I analyzed the data, there was no DNA profile. I went back and took another cutting, and still no profile. I had other DNA results in the case, so I didn’t go back a third time, but the re-analysis extended the turnaround time for that particular case.
  • At every stage in the entire process, positive and negative controls are used to ensure that quality results are obtained. If the controls fail or do not work properly, the samples associated with those controls need to be re-run.

Troubleshooting instruments can also interfere with getting timely results. Not only is the instrument out of commission, which can interfere with productivity, but someone has to troubleshoot with tech support to figure out the problem (which means that analyst isn’t doing casework). I once had to troubleshoot a genetic analyzer for three weeks! Other cases were being worked by other analysts, and I was able to tech review cases in between troubleshooting tasks, but I was not working new cases during that time.

Availability of crime lab personnel can have a major effect on turnaround time. People go on vacation, attend trainings/conferences, get sick, have medical/family emergencies, go on leave, and so on. Lack of personnel hits a smaller lab (like the one I worked at) especially hard. If someone resigns, the position isn’t filled right away (it can take months), and when it eventually is, someone has to train the new person, taking the trainer away from casework.

In my old lab, the technical review step was often a bottleneck. If someone put a casefile in my inbox, it usually took me several days (if not a week or more) to get to it. Forensic scientists have other duties in addition to casework, such as meetings, court, presentations, instrument maintenance, audits, and trainings.

Cases were also delayed if we were waiting for information from the submitting agency or prosecuting attorney. We would often have to call and ask questions prior to completing our analysis. If they didn’t respond in a timely manner, the case would sit until they did.

So now that you know what can affect a case and have a realistic idea of real-world turnaround times for DNA cases, how should you implement this in your books?

What Turnaround Time to Use for DNA Analysis in Your Books

If a lab didn’t have a backlog, 30 days is a reasonable time to get DNA results back for a medium-sized case with no re-analysis. If this doesn’t fit with your book timeline, you could maybe say two weeks. You could also have the agency pay to send the evidence to a private lab for testing. Private labs have quicker turnaround times, and agencies can pay rush fees to have the case expedited and you could say a week for those results. Just keep in mind that the agency would need to prioritize the items (which means they can’t send in everything, especially in a bigger case).

Cases can be rushed at traditional crime labs, which means they move to the front of the line. The rush policy at every crime lab is different (but you could make it up for your story). Homicides are typically prioritized (and they take the most time), although in a bigger city with a high number of homicides, it still might take a while. Cases with upcoming court dates are also rushed.

Do you have any other DNA turnaround time questions that you need answered for your book? Ask in the comments below!




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