DNA and Evidence Collection Principles
Robert E. Kramer - Detective
Police Division - 220 Clay Street
Cedar Falls, IA 50613
(319) 268-5132
fnewsia@mchsi.com
The dawn of a new age has arrived in law enforcement in the form
of DNA research and testing. We in law enforcement, especially
those of us working the crime scenes need to be aware of what we
can do "in the field" to assure that proper evidence
collection techniques are followed. Only then will the groundwork
for successful evidence examinations be in place when we submit
the case to a forensic laboratory for analysis.
Polymerase Chain Reaction
Polymerase Chain Reaction (PCR) is the DNA evidence analysis technique which is being practiced at the state laboratory at the Division of Criminal Investigation in Des Moines. PCR is a sensitive, fast, and highly discriminatory method of analysis. One of the most essential aspects of DNA evidence analysis at the lab is that a basis knowledge of evidence collection principles is necessary at the initial stage. PCR allows the criminalist to examine evidence which has been properly collected and preserved with expectations that accurate results will be found as result of the analysis.
Impact and Exchange
It is widely embraced within the law enforcement forensic field that, to at least some degree, the process of impact and exchange occurs at every crime scene. For example, a "run" vehicle impacts the accident scene and exchange occurs with the transfer of paint to the victim vehicle; a burglar impacts a scene with the approach of the area, and exchange occurs when footwear impressions are left behind. As law enforcement officers and crime scene specialists, it is our job to collect and preserve evidence at the scene - evidence which may not only connect the suspect to the scene - but connect the suspect to the incident itself.
Swab Method
The collection and preservation of evidence which will be subjected to DNA analysis is best accomplished by the seizure and submission of the original item. For example, it would be desirable to collect and submit undergarments worn after an incident involving suspected sexual assault rather than cutting or swabbing the specimen. Sometimes, however, the submission of the original item is impossible or impractical. Imagine a shooting or stabbing scene where there is evidence of considerable blood loss on a tile or linoleum floor. The practice of swabbing for the evidence is then practical for collection of possible DNA evidence.
It is preferred that swabs to be submitted to the D.C.I. Lab in Des Moines be made with cotton tipped swabs (ie: Q-tiptm). The process is simple, and the following outlines the procedure:
(2) Air dry - NEVER use a hair drier.
(3) Package separately in paper (no plastic containers).
(4) Keep out of direct sunlight.
Eliminating the chances of cross, sample-to-sample, or collector contamination cannot be stressed enough. There are steps which can be taken in advance which will both: a) make the job easier, and b) reduce and possible eliminate that chance of evidence contamination.
Preparation is the key word when it comes to DNA evidence collection. You wouldn't wait until the night of a multi-thousand dollar safe burglary to order footwear casting and fingerprint supplies from the manufacturer would you? Some very low cost supplies can be obtained in advance which will "keep" for a considerable period of time. Paper, plastic, or wooden shafted swabs all work fine, but the durability of the wooden shaft swabs should be considered. A styrofoam block should be obtained and kept in your evidence collection kit. The wooden shaft swabs can be placed, shaft end down, in the block and allowed to dry. Prior to doing so, you may want to affix a piece of double side sticky tape on the bottom of the block to prevent it from tipping over as the swabs are attached to it. Small adhesive labels can be purchased and attached to the swab (prior to the sample being collected) which can be used to identify the swab. When the swabs are dry they should be placed in separate paper envelopes for preservation. Plain letter envelopes work well, although manilla or glycine envelopes are equally suitable.
The cotton swabs, a small glass jar (with a secure lid) of water, latex gloves, envelopes, stickers, a marker, and the styrofoam can be packaged neatly in a tackle box. (I prefer a $1.49 plastic pencil case purchased at the local discount department store). NOTE: In the interest of really saving time at the crime scene, package the swabs in individual envelopes in advance. This reduces handling the swab at the scene - and if using manilla envelopes, place the swab tip-side-down so that it may be removed from the envelope without handling the cotton end.
Tape Lift
Dried blood samples can be conveniently lifted from non-porous surfaces with conventional fingerprint tape. This process is beneficial in that the very size and shape of the stain may in fact be preserved on the lift. Of course, the lift should be placed sticky side down on a piece of plain white typing paper. It is suggested that paper be used (in lieu of plastic or fingerprint backing material) due to the fact that the paper will allow the specimen to "breath" As with the swab, the lift should be packaged in a separate envelope.
Control Samples
When conducting DNA analysis, the criminalist needs to have a "control" sample to compare with the suspect swab/evidence. For this reason, the crime scene examiner needs to document, collect, and preserve a control sample with the same care that the suspect sample is treated. For obvious reasons, it is suggested that the control sample be collected prior to the suspect sample. By collecting the control sample first, there is less chance of contaminating it with the blood or other biological fluid as the subsequent samples are being collected. Also make sure the same water is used to collect both the control and evidence samples. Finally, if cuttings of a suspected sample are being submitted for analysis (ie: a couch) it is preferred that the control samples also be cuttings, rather than swabs or merely fibers.
Other Evidence
Known biological specimens can be collected from both living and deceased persons easily, and we have been doing so for years in the form of sexual assault kit supplies. Known blood in quantity should be collected and preserved in one of the three following tubes:
Cheek swabs can be collected from individual and may in fact result in the discovery of some of the most highly concentrated DNA cells. The cheeks swab is non-threatening, in that the individual feels less intimidated by the process. The procedure is quick and simple:
Deceased Individuals
Common sense and knowledge of previously approved practices seem to be the rule when deceased individuals are concerned, particularly when severe decomposition is present and blood work not practical. If hairs are to be submitted, make sure the collector obtain pulled hairs. The tissue associated with the hair root is needed in the DNA analysis. Other samples which may be suitable for DNA analysis include: bones (rib or long bones preferred), teeth, muscle tissue, and associated property which may be found with the body (hairbrush, toothbrush, etc.)
Questioned Evidence
The following are being submitted as miscellaneous tips which should be considered prior to and during the DNA evidence collection process....
positive considerations
negative considerations
Wear protective outer clothing, as well as the standard latex gloves. Since the crime scene examiner is subjected to exposure to elements, it is recommended that the outer clothing be changed upon returning to the scene after leaving.
Finally - maintain the samples at ambient conditions or cooler. Room temperature is acceptable, refrigeration is desirable, and freezing is preferred.
REMEMBER - practice common sense. Don't let the collection of biological evidence be intimidating. If sound procedures are followed, successful and thorough crime scene work can be accomplished in a safe manner, with valuable evidence in hand.