DNA evidence is becoming more and more important in all kinds of criminal investigations. But if it’s been a few years since your last biology class, the science might be intimidating. It doesn’t have to be!
- What DNA is
- Why it’s such a powerful tool to identify people in criminal investigations and cases
- How DNA interpretations are performed
- the basic statistical analysis that gives DNA evidence meaning.
JCH Editors: Roxanne, you’re new to the Justice Clearinghouse audience. Can you tell us more about yourself and how your partnership with prosecutors like Chris is can be an asset for trying cases?
Roxanne Kotzebue: I’ve been at the San Diego Police Department for four years and have the opportunity to be part of a lab that utilizes many great techniques in DNA casework, such as using male DNA to screen sexual assault evidence, analyzing spent cartridge casings for DNA, and using the latest technology to help interpret DNA results. Our lab is dedicated to representing the evidence. One of the responsibilities I have as a Criminalist in a forensic lab is to explain what the results from the evidence mean. Sometimes that explanation is directed at prosecutors, but it is also to our other end users, such as detectives, defense attorneys, or a jury.
JCH: Your presenting partner, Chris Lindberg, just presented about DNA Basics and understanding the use of DNA evidence in criminal investigations and prosecutions. How is this webinar different? How does it build on the previous webinar? Do people need to have attended the first webinar in order to understand this one?
Roxanne: Attendance to the first webinar, by DDA Chris Lindberg, is not necessary to understand the current presentation. Basics of biology and DNA will briefly be covered, while the main focus of this new webinar will be the science behind body fluid identification, DNA analysis, and future trends in forensic DNA analysis.
We do our best to educate officers and detectives
about best practices to preserve DNA evidence
and we like them to know about the possibility of evidence contamination.
JCH: Shows like CSI and the advent of DNA genealogy companies like 23 and Me or Family Tree have brought the idea of DNA out into the average person’s awareness. That’s not a bad thing –But I’m sure there are misunderstandings about DNA as well. What do you wish more law enforcement officers knew about DNA evidence?
Roxanne: Our law enforcement officers do an excellent job of collecting evidence and understanding that our analysis takes longer than 30 minutes, like we see on TV shows.
We do our best to educate officers and detectives about best practices to preserve DNA evidence and we like them to know about the possibility of evidence contamination. At the crime scene, people should avoid talking over the evidence item, should wear and change gloves between items, as well as store the evidence in a paper bag rather than plastic.
Another important thing to consider when collecting evidence is who potentially touched the object and collecting the appropriate references. For example, if someone broke into a victim’s house and moved an object, a reference from the victim would be helpful in resolving a mixture that may be obtained from the item.
Companies that perform DNA analysis either for familial or health screens do not focus on the same areas on the DNA strands as forensic scientists. The areas of DNA that our forensics lab tests do not give us any information regarding health, appearance, or ancestry. Once DNA results are obtained from the evidence, we have to do a comparison to a reference; the profile will not simply tell us who an individual is. There are technologies provided by other companies, such as Snapshot, that advertise using specific DNA markers to predict ancestry, hair and eye color, and facial reconstruction. This newer technology has the potential to help develop investigative leads if there are no eyewitnesses to a crime.
Overall, I am impressed with the dedication of law enforcement to understand DNA, maintain proper collection and storage techniques, and assess the evidence to send the most probative samples for DNA analysis.
At the crime scene, people should avoid talking over the evidence item,
should wear and change gloves between items,
as well as store the evidence in a paper bag rather than plastic.
JCH: What are the biggest misconceptions prosecutors have or deal with regarding DNA evidence?
Roxanne: One factor that prosecutors tend to forget is the laboratory’s workload and the time required for analysis. The laboratory often carries a backlog of requests for analysis, meaning that we have more work than we can handle on a regular basis. Often prosecutors will request additional analyses in the days before a preliminary hearing or trial. We try our best to accommodate those requests, but the lab cannot always meet the time requirements. Not only does the lab need to complete the analysis, but a report also needs to be produced and then reviewed prior to being issued. Providing the lab with as much time as possible is appreciated.
We generally find that prosecutors are trying to answer the larger legal questions of guilt or innocence of particular crimes. DNA analysis generally does not provide the answer to those higher level questions. Rather, DNA analysis attempts to answer the question of whether a person’s DNA is on a particular piece of evidence. Prosecutors generally expect a “yes” or “no” answer to that question, but the analyst provides an answer framed in probabilities, not certainties. Certain probabilities are convincing enough to infer definitive contribution, but some may not be as strong.
The presence of a person’s DNA on an item does not answer the question of how it came to be on the item. Understanding the context of the DNA analysis is important. If a person is included as a possible contributor in a mixed DNA sample, there are numerous factors that must be considered before determining the meaning of that result. Factors such as what the item is, where the item was found, and whether the item is something the individual would have contact with outside the context of the crime, are all questions that the legal community should be considering when reading reports generated by a forensic lab.
Click here to Watch “The Science of DNA – Simplified! What Law Enforcement and Affiliated Professionals Need to Know.“