Criminalistics Laboratory - DNA Casework Section

The DNA Section consists of two units. They are as follows:

• The DNA Casework Unit provides examinations to law enforcement agencies at no cost. Items from criminal cases are examined for the presence of human DNA. DNA can be found in biological fluids, tissues and bones of the body. If DNA profiles are obtained from samples in question, comparisons may be made to known DNA profiles from individuals believed to be involved.

• The DNA Profiling Convicted Offender Unit (PCO) determines the DNA profiles of convicted offenders and stores their profiles in a computer database. Comparisons are made between the profiles found in the convicted offender database and the profiles obtained from criminal cases where no suspect has been identified.

*Please fill out the DNA Case Information Form when submitting DNA evidence.

What is DNA?

DNA is an acronym for the genetic material deoxyribonucleic acid. DNA is used by the body to determine whom an individual is, everything from physical features to personality.  DNA is found in all nucleated cells of the body.  One half of a person’s DNA comes from their mother and the other their father.  This combination is what makes an individual unique with the exception of identical twins. The DNA found in an individual's blood is the same DNA that is found in their saliva, tissue, bone, etc.

What is DNA testing?

DNA testing or "profiling" is used to identify a potential source of biological evidence by matching questioned samples (left at crime scenes) with known samples from victims and suspects. For example, when a sexual assault occurs and seminal fluid is left on the vaginal samples of the victim, it is possible to compare the DNA profile obtained from the semen donor to a known DNA profile from a suspect. Since the DNA profile from the suspect's semen will be the same as that of his known saliva or blood, a match will link a suspect to a crime.

What can be tested?

Blood and semen are most commonly tested but they are not the only possible sources of DNA. Saliva, sweat, vaginal fluid, hair (with suitable root structure), muscle tissue and bone may also be tested. Urine and fecal samples may contain small quantities of DNA but are poor sources for testing.

How should samples be collected?

All samples should be collected using appropriate collection procedures to avoid sample destruction or degradation. Additionally, every precaution should be taken to avoid contaminating the biological sample upon collection.  Biological material is best preserved in a dry, cold environment. All items should be packaged separately into paper bags or envelopes. 

DNA Evidence Collection at Crime Scenes is a pdf file containing information from the Criminalistics laboratory regarding the collection of evidence.

For more information on collecting and packaging biological samples please visit the following website:
https://www.fbi.gov/file-repository/handbook-of-forensic-services-pdf.pdf/view

How should known reference samples be collected?

Known reference samples are most commonly submitted as either buccal swabs or as dried blood samples. When possible, known reference samples should be provided at the same time as the questioned evidentiary material. (Submitting agencies, please state on the case submission form if no known suspect sample is available and why.)  Buccal swab(s) should be collected by scrubbing a clean and dry cotton swab on the inside surface of the cheek and gums. It is advisable to collect at least two swabs and to allow the swabs to air dry in a breathable swab box, paper envelope, or appropriate container.  Identify the buccal swabs with the appropriate information and submit them to the lab in a timely fashion. The dry buccal swab does not need to be refrigerated. The known dried blood sample should be collected by drawing blood (by qualified medical personnel) on to a filter paper card using a finger stick collection device and having the blood sample blotted off the fingertip on to an appropriate filter paper card and air dried.  Place the dried blood card into a paper envelope and seal.  Identify the blood sample with the appropriate information and add biological identifier/hazard labels as appropriate.  The dried blood sample does not need to be refrigerated.  Submit the sample to the lab in a timely fashion.

What type of DNA test is performed?

Nuclear DNA testing is the method utilized by the Iowa DCI Crime Lab.  Meaning that the DNA used for testing is found in the nucleus of a cell.  The technique used to profile the DNA is called the Polymerase Chain Reaction (PCR). PCR allows millions of copies of very specific areas on the DNA molecule to be obtained. This process known as "amplification" is a powerful scientific tool because it allows very tiny amounts of DNA (which may have been left behind as evidence of a crime) to be successfully analyzed. Commercially purchased DNA typing kits are used to analyze as many as twenty-three Short Tandem Repeats (STRs). STRs are genetic markers that vary in size among individuals. Their small size (typically 4 bases per repeat) makes them excellent for use with PCR and also makes them less susceptible to degradation. The STR tests are currently the most widely used DNA tests in the forensic community.

How long will testing take?

DNA testing involves a series of steps. First the item is examined for biological fluid stains or other possible sources of DNA. 
Once a source is found it is identified as seminal fluid, blood, etc. The DNA is then extracted from the sample, quantified, subjected to PCR and profiled using automated instrumentation. This process is greatly affected by the number of samples that need to be tested. In general, PCR testing can be completed within one month after a case is started, however, current backlogs may make this turn-around time longer.

How specific are DNA "matches"?

STR matches are very discriminating for single-source samples. Typically, a complete DNA profile is estimated to occur in less than one out of one hundred billion random, unrelated people. In cases where complete DNA profiles cannot be obtained, the profile's frequency of occurrence becomes more common.

What can be done with mixtures of DNA from two or more people?

This situation is commonly encountered with sexual assault evidence. DNA extraction procedures are used to separate sperm cell DNA from non-sperm cell DNA. In many cases this is successful and a clear profile of the perpetrator can be obtained. Sometimes complete separation cannot be obtained and the perpetrator's sperm cell DNA will be mixed with the victim's DNA. Blood-blood and semen-semen DNA mixtures can also occur. The ability to distinguish individual contributors to a mixed DNA profile will vary from case to case, and is highly dependent upon the relative quantity of DNA contributed to the mixture by each individual.

Are samples consumed in the process of DNA testing?

The amount of sample that is required for testing is minimal, so typically only a small fraction of larger sized stains are consumed by testing. This allows independent testing to be performed should the defendant(s) choose to do so. When insufficient sample is available for independent testing the extracted DNA will be stored at the crime lab.

Should cases without suspects be submitted?

Yes. "No Suspect" crimes against persons should be submitted for testing. In many cases DNA evidence left at the scene may be the only link to potential perpetrators. The DNA profiles obtained from "No Suspect" cases may be placed into a computer database and searched against DNA profiles from convicted offenders as well as evidentiary samples from additional "No Suspect" cases.  Submitting agencies, please state on the case submission form if “no suspect is identified”.

What is CODIS?

The Federal Bureau of Investigation facilitates the use of a national DNA database called CODIS. CODIS is an acronym for the Combined DNA Indexing System. It may be utilized for DNA profile searches within the state of Iowa as well as across the United States. DNA profiles uploaded to CODIS with less genetic information may only be searched within the state of Iowa.

CODIS has proven to be an effective tool for providing investigative leads to law enforcement agencies. This is particularly true when no suspect has yet been developed. Upon entry into CODIS a DNA profile may be compared to DNA profiles obtained from Crime Laboratories across the country for potential matches. This exchange of information allows a DNA profile from one crime scene to be linked to a separate crime scene in a different jurisdiction. Additionally, CODIS eligible DNA profiles will also be compared to DNA profiles obtained from individuals convicted of qualifying offenses.

When a DNA match is found in CODIS and it provides information that the case officer previously did not know, it is called a “hit”. When a CODIS hit occurs, a CODIS match report may be issued to the agency or agencies involved. There are two types of CODIS match reports, the Forensic hit report and the Offender hit report. A Forensic hit report is issued when a DNA profile from a crime scene matches a DNA profile obtained from a separate crime scene. An Offender hit report is issued when a DNA profile from a crime scene matches a DNA profile obtained from a convicted offender.
As the number of profiles in convicted offender databases increases, the number of "cold hits" or matches to "no suspect" cases increases. Currently, enormous backlogs of convicted offender samples are unanalyzed in the USA. Substantial reduction of these backlogs is expected in the next few years depending on available funding.
 

What qualifies as a CODIS eligible DNA profile?

A DNA profile becomes CODIS eligible when it is obtained from biological material collected from a crime scene and is attributable to a presumed perpetrator.

To assist the laboratory in determining whether a submitted item may be eligible for CODIS, the laboratory requests that submitting agencies provide a specific description of where the item was collected and to whom the item belongs if known. This description should be recorded on both the outer packaging of the item as well as the evidence pre log. Until this information is provided by the submitting agency DNA profiles may NOT be eligible for entry into CODIS.  Please fill out the DNA Case Information Form when submitting DNA evidence.

Providing sufficient detailed information about a submitted item will expedite its entry into CODIS. The following list shows descriptions of preferred wording to use when submitting items for DNA testing:

• “The swab of blood was collected from the point of entry/exit at the burglary scene. The victim states that the blood is not theirs and was not there prior to the incident.”

• “The cigarette butt was collected from inside the burglary victim’s residence. The victim is a non-smoker.”  

• “The suspect’s mask was collected from the path of exit from the bank. The mask does not belong to any of the employees or anyone in the bank at the time of the burglary.”

• “The beverage container was collected from inside the victim’s vehicle. The beverage container does not belong to the victim.”

• “The gloves were collected from inside the victim’s residence. The gloves do not belong to the victim.”

Additionally, please describe any known relationships between the victim and suspect (husband/wife, boyfriend/girlfriend, etc). Submitting agencies are encouraged to provide this information in the "Case Comments" section of the pre log.
 

What items are ineligible for CODIS entry?

Please be aware that some items submitted for DNA testing may not be eligible for entry into CODIS. To become eligible for CODIS an item must be collected from a crime scene and also be attributable to a presumed perpetrator. The following are examples of submitted items that would not be eligible for CODIS:

• DNA profiles obtained from known reference DNA samples. Known reference DNA samples are items such as buccal swabs (note: buccal refers to the inner oral cavity) and blood cards collected directly from individuals believed to be involved with the case. Known reference DNA samples should be provided when possible for comparison purposes. However, because these items are not crime scene evidence they cannot be entered into CODIS.

• A suspect puts out a cigarette in an ashtray at a restaurant and the cigarette butt is submitted for DNA testing. Assuming the suspect has not committed a crime while eating lunch, the cigarette butt is not crime scene evidence and therefore ineligible for CODIS entry.

• A victim’s DNA profile is obtained from stains located on the suspect’s bloodstained shirt. This information may be of probative value for investigative purposes, but because the victim is not the presumed perpetrator for the case, the DNA profile obtained from the shirt is not eligible for CODIS.

• A suspect’s DNA profile is obtained from bloodstains found on the suspect’s own item of clothing. Because the clothing was seized directly from the suspect, DNA profiles obtained from such items are not eligible for entry into CODIS.

• An incomplete or “partial” DNA profile may be obtained from an item deemed CODIS eligible. However, because the DNA profile was not complete, there may not be sufficient data to support entry into CODIS.