Q: What kind of blood tube is needed for DNA analysis?
A: A purple-capped (EDTA) blood tube is preferred. Alternately, a buccal swab (swabbing of the interior cheek) may be used as a reference standard.
Q: What does the expiration date on the sexual assault kits mean, should they be thrown out if they are expired?
A: The expiration date on the sexual assault kit refers to the blood tube only. If the blood tube has expired replace it with a purple-capped (EDTA) blood tube from the hospital stock. Do not discard the kit!
Q: Why do I need to submit standards from my suspect(s) and victim(s)?
A: It is incumbent upon the DNA section to make every reasonable effort to associate biological stains with the individuals who may have imparted the stain. Due to the sensitivity of current DNA procedures, it is not uncommon to find mixtures of DNA on an item. An example of this would be finding the suspect's blood on the victim's clothes. Simply being the wearer of the clothing, the victim may impart their own DNA on the garment, thus causing a mixture with the suspects DNA. If we only had the suspects standard to compare to the stain, there would always be a question as to who else's DNA is present unless we had a standard from the victim as well.
Q: What is meant by a standard?
A: A standard is a reference biological specimen from a known individual. Obtaining a standard from a known individual is similar to obtaining a ten-print card for fingerprint comparison. Intravenous blood and buccal swabs (swab from the interior cheek) are appropriate standards to use for comparisons.
Q: What is a secondary standard and why don't you use secondary standards for comparison?
A: A secondary standard is a reference standard that is not an intimate sample such as intravenous blood or buccal swabs (swab from the interior cheek). Secondary standards are normally items that have used by the person such as a toothbrush, used dental floss, shaving razor and or a cut from a suspect’s hand. We generally do not like to use these items as standards because we cannot always ensure that these items came from the person in question. If an appropriate standard is available we will always request that over a secondary standard. In circumstances where an appropriate standard is not available, such as missing persons, mass disasters or interred bodies, we will consider using a secondary standard.
Q: What type of education is required for employment?
A: The DNA section requires its analysts to possess a baccalaureate degree in one of the natural sciences (eg. Biology, Chemistry, Forensic Science); coursework must include 20 semester hours in biology (course credit in genetics, biochemistry, molecular biology, recombinant DNA technology or other subjects which provide a basic understanding of the foundations of forensic DNA analysis should be included in hours. Course credit in statistics and/or population genetics is recommended.
Q: How do I submit evidence to be tested by the laboratory?
The Saint Louis County Police Crime Laboratory (SLCPD) will accept evidence from any law enforcement agency, regulatory agency, or law enforcement function branch of an agency in or of the State of Missouri or the Federal Government of the United States.
All evidence received must be associated with a criminal investigation. Evidence associated with civil litigation will not be accepted.
DNA evidence and reference samples will be accepted according to the criteria outlined in the SLCPD DNA Submission Guidelines
All evidence received by the SLCPD Laboratory must be properly sealed. A proper seal is defined as closure of the container by any number of various sealing devices which will protect the contents from loss, cross transfer, contamination or degradation during routine handling. The seal should be such that entry into the container will result in obvious damage and/or alteration to the container or its seal and is further authenticated by the initials or identifying mark of an individual responsible for the container's contents.
Evidence that is too large to be sealed (vehicle body parts, mattress, house doors, etc.) will be stored in a secure area of the laboratory and examined as soon as possible.
The Laboratory will not repeat or duplicate forensic examinations that have previously been performed by another laboratory. Supplemental testing that has not been performed on previously examined specimens will be conducted only if the evidence may provide additional probative value to the case and after discussion with Prosecuting Attorney.
Generally all evidence, and samples collected from evidence, will be returned to the submitting agency (County cases are maintained by the Property Control Unit) when the forensic examinations are completed.
Q: Do you do paternity testing on criminal cases?
A: Currently we do not perform paternity testing. We will assist in packaging and submission of samples to an outside laboratory for testing.
Q: Can I use tap water to collect a bloodstain?
A: The appropriate and preferred source of water would be distilled water on a sterile swab. Bottled water purchased at a convenience or grocery store may be considered distilled. If an appropriate water source is not available, tap water would be acceptable.
Q: Why does it take so long to get the results of my case?
A: The DNA section of the SLCPD Lab services Saint Louis County and over 90 municipalities. As a matter of routine, we work cases on a sequential basis. Often times it may be several months in duration before we actually begin a particular case. If a case necessitates being expedited, please contact the laboratory director or DNA supervisory staff to present your request.
Q: Why don't you just do DNA on all of my samples, not just the ones you pick?
A: DNA evidence is best used to make good associations between victims, suspects, and crime scenes. As DNA testing is very expensive, it is our position that we generate as many associations as possible using the least amount of resources and evidentiary material.
Q: Why do the reports contain so much unnecessary information? All I want to know is whether it is a match or not.
A: Due to our accreditation and laboratory policy, we are required to include much more information in our reports than may seem necessary to the casual observer.
Q: What do the statistics in my report mean?
A: Since we do not look at the entire DNA molecule and only look at a small portion, we apply a frequency statistic on the genetic loci (locations) that were observed in order to give us a statistical measure of how often we could expect the observed genetic pattern or profile. In other words, we attempt to report statistically how frequent or rare it would be to randomly encounter the questioned genetic profile (or pattern) at all of the genetic areas tested. This type of estimation is very similar to various statistical measures many of us may use in our daily lives, such as knowing that the frequency of obtaining a heads when a coin is flipped would be 1 in 2; or obtaining a six on a six-sided die would be 1 in 6.
Q: Why can't I package items in plastic?
A: Biological specimens inherently harbor bacteria. Bacteria grow in warm and moist environments. Packaging biological specimens in plastic would encourage bacterial growth by allowing the specimen to stay warm and moist, a greenhouse effect. Packaging in paper (or cardboard) will allow the specimen to breathe and will take away the one thing that bacteria need most, moisture. Packaging in paper and keeping the specimen cold (or frozen) is the most suitable way to attenuate bacterial growth.
Q: Can DNA analysis be done on hair?
A: Yes, hair does contain DNA. Due to the cost of DNA analysis, we process hair only in cases where no other evidence exists. If the root of the hair is in its active growing stage, DNA may be extracted from the root. If the root is not in its active growing stage and naturally shed, then the hair would be a candidate for mitochondrial DNA analysis. The SLCPD lab DOES NOT perform mitochondrial DNA analysis.
Q: What is mitochondrial DNA testing?
A: The SLCPD Crime Laboratory performs DNA testing on DNA extracted from the nucleus of the cell (nuclear DNA). Mitochondria are organelles in the cell that maintain their own autonomous genome. Mitochondria are in much greater abundance than the nuclei of the cell and therefore biological specimens will contain much more mitochondrial DNA. In particular, hair and bone tissue that do not contain nuclei and therefore do not have nuclear DNA and would subsequently lend themselves well to mitochondrial DNA testing.
A distinct advantage of mitochondrial DNA testing is that the mitochondrial genome is maternally inherited and does not undergo recombination (hemizygous); therefore the mitochondrial DNA is very useful in comparing maternal lineages. This can be very valuable in missing person's cases or found body cases. If mitochondrial DNA testing is recommended the SLCPD laboratory will assist in obtaining that testing.