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Property Crime Sample Processing: Law Enforcement Experiences and Crime Laboratory Efficiencies
Careful attention to sample collection and improved extraction methods coupled with implementation of enhanced amplification systems will greatly benefit laboratories seeking to harness the power of DNA evidence for property crime samples.
As more law enforcement agencies begin to utilize DNA technology for non-violent crimes, challenges emerge. Law enforcement officers must be trained to gather and submit the most probative evidence from a growing number of crime scenes, while crime laboratories must streamline and refine existing workflows to accommodate an increased number of challenging samples. These requirements necessitate close collaboration between the law enforcement and scientific community to successfully embark upon a new era of criminal investigation.
Law Enforcement Experiences
DNA is a powerful law enforcement tool. Less than ten years ago, in major cities such as New York, crime scene investigators recovered DNA only in high profile violent felonies primarily associated with homicide and sexual assault investigations. Other felonies, such as assaults where the victim was not likely to die, robberies, criminal possession of a firearm, grand larceny auto theft, possession of a controlled substance, and property crimes including both residential and commercial burglaries were only routinely forensically processed for the presence of latent and patent fingerprints.
In September 2003 the New York Police Department (NYPD) implemented a pilot program titled “Biotracks” that was funded by the President’s DNA Initiative Program administered through the National Institute of Justice and New York State’s Division of Criminal Justice Services to solve no suspect burglary cases. The NYPD recovered the DNA evidence from no suspect burglary scenes, vetted the cases, and forwarded them to selected private vendors for analysis. The vendors then forwarded their analytical reports to the Office of The Chief Medical Examiner’s Biological Laboratory (OCME) for technical review. Applicable DNA profiles were uploaded into the CODIS system by the OCME. Match results were then forwarded to the NYPD for investigation. By generating DNA profiles from evidence collected at burglary scenes and uploading them into the local, state, and national DNA databases, perpetrators of no-suspect cases were identified and links between otherwise unrelated burglaries were established.
The Biotracks program, which expanded in September 2005 to include all areas of New York City, continued with tremendous success until its conclusion in 2008. During this period, over 3,430 crime scenes were processed in which 6,391 items of DNA related evidence were recovered. Partial statistics revealed that as of April 2008, 1,558 CODIS-eligible profiles were generated, leading to 692 case-to-offender matches to 548 offenders. The vast majority of offenders pled guilty and received substantial sentences. The program revealed that many of the offenders were recidivists whose arrest records indicated the crime of burglary was a common denominator and that burglary was often a stepping stone to more serious crime. The Biotracks Program became a model for how all crime scenes are now processed. Today in NYC, all crime scenes including homicides, sexual assaults, robberies, property crimes, gun possession, and auto theft are forensically processed for both fingerprints and DNA when applicable.
In addition to the success of the Biotracks program, other studies have shown the value of expanding the use of DNA to a broader range of crimes, specifically property crimes. In fact, a previous study by the National Institute of Justice found that, when DNA was collected from property crimes, arrests and identifications doubled, as did prosecutions. Also, according to the NIJ,more suspects were identified using the FBI’s DNA database than the fingerprint database (Roman, J.K., et al. 2008. The DNA Field Experiment: Cost-Effectiveness Analysis of the Use of DNA in the Investigation of High-Volume Crimes,Urban Institute Justice Policy Center).
Transitioning to a New Era
There is little doubt that collecting and processing a broader range of evidentiary material is the right thing to do. It saves investigative time and tax payer dollars, while being more efficient than utilizing traditional investigative methods alone. However, it’s more complicated than that. A series of protocols and trainings must be implemented in order to collect, preserve, process, and store an increasing number of samples. These must be guided by the best practices of the law enforcement and scientific communities to ensure robust, quality processes are established, beginning with understanding what is most important to collect.
Probative and Non-Probative Evidence
The crime laboratory and evidence collectors should work closely together to establish processes at a crime scene that distinguish between probative evidence and non probative evidence. Probative evidence is evidence recovered from a crime scene that would provide the case investigator probable cause to make an arrest. It is evidence that would prove or disprove an alleged fact relevant to the investigation. Non probative evidence is evidence recovered from a crime scene that would not provide the case investigator probable cause to make an arrest. However, it may provide the case investigator with an investigatory lead or it may be evidence that, at a later date,would prove significant to the investigation. Crime scene investigators must be trained in the recognition and collection of probative evidence and the ability to differentiate probative from non-probative evidence. Evidence collectors must be trained to not over burden their crime laboratories with non probative evidence.Once probative evidence is identified, it must be collected and submitted for analysis.
Preserving and Safeguarding a Crime Scene
There are numerous considerations for crime scene personnel in the collection and storage of DNA evidence including:
- Prevention of contamination through the use of personal protective equipment and clean instruments in addition to not touching other objects (including their own bodies)when handling evidence or the items used to collect the evidence.
- Protecting the chain-of-custody of the DNA evidence through proper documentation.
- Use of appropriate techniques for DNA evidence collection.
- Proper packaging, transport, and storage of DNA evidence to minimize the potential for degradation.
These considerations are discussed in detail elsewhere (Blozis J: Forensic DNA evidence collection at a crime scene:An investigator’s commentary; Forensic Sci Rev 22:121; 2010).
Collecting Touch DNA Evidence. Touch DNA exists where a perpetrator has touched a surface at the crime scene, possibly leaving a fingerprint as well as DNA. Having the proper supplies on the scene, and the knowledge to use them, is critical to the collection of usable DNA samples. A crime scene investigator’s toolkit should include basic and necessary supplies to recover DNA evidence from crime scenes.The supplies that are normally used for processing and recovering DNA samples include sterile cotton-tipped applicators (swabs) on which to collect samples, sterile water or a phosphate saline solution to moisten the swab prior to collection, and plastic pipettes to transfer the sterile water to the swab. Proper swabbing techniques for touch DNA are described in Figure 1. Helpful processes for swabbing biological materials are detailed in Figure 2. In addition to swabbing, samples may be cut from items or scraped from surfaces. Conferring with laboratory personnel may help to establish which collection method is preferred for a particular type of evidence.
Crime Laboratory Efficiencies
Once the evidence has been collected, documented, and packaged, it is transported to the laboratory for analysis. The effectiveness of property crime programs to reduce crime and the visibility that such successes have achieved has increased the prevalence of property crime sampling and submission. This makes it imperative for laboratories to maximize efficiencies.
Property crime samples present unique challenges to the forensic biology laboratory workflow. Such samples are commonly submitted as swabs that have been collected at the crime scene by police officers or crime scene technicians and may preclude an independent evaluation of the primary substrate for stain pattern and body fluid type. The conditions under which the sample was collected may not be evident to the forensic analyst leading to a series of questions to determine the probative value of the sample as previously described. Once the possible probative value is established, sample evaluation may consist of:
- Visual examination for the presence of possible blood
- Assessment of potential inhibitory substances in the form of obvious dirt, dyes, or discoloration; substances such as hematin from blood, humic acid from soil and dyes, such as indigo, used in various fabrics are well known inhibitors of PCR
- Presumptive testing for the presence of blood or saliva (as dictated by the case)
Of primary importance is whether human DNA of sufficient quality to generate a genetic profile can be recovered from the swab material. Given the wide variety of sample substrates which may serve as a source of DNA, the use of a sample extraction method which maximizes the removal of inhibitory substances is recommended. Fortunately for laboratories, the standardization of property crime sample collection on cotton swabs renders the extraction procedure easily amenable to automation, allowing labs to process these higher sample volumes.
Several magnetic bead-based chemistries and analytical methods meet the criteria for high throughput property crime sample processing in a dedicated workflow. Such methods involve the following steps:
- Hydration of the swab substrate in a lysis solution, typically containing detergents, such as sodiumdodecyl sulphate (SDS), and Proteinase K, or a high concentration of a chaotropic salt such as guanidiniumthiocyanate (GuSCN), to effect the disruption of cell membranes and release of the DNA into a liquid form.
- Complexing of the DNA to the magnetic particles.
- Washing the DNA/magnetic particle pellet to remove cellular materials and PCR inhibitors.
- Elution of the purified DNA from the magnetic particles.
These methods are easily automated on high-throughput liquid handling systems and many of these have been validated for use with a wide variety of forensic sample types. Magnetic bead-based extraction methods routinely produce high quality DNA extracts from even very low amounts of biological material and yield easily interpretable DNA profiles.
Enhanced Amplification Methods
A subset of samples, however,may prove to be particularly challenging due to the failure to effectively remove inhibitors, the presence of more than one DNA contributor, or the recovery of extremely limited amounts of biological material. In order to address this, laboratories are increasingly moving toward amplification chemistries with enhanced capabilities in the effort to provide higher quality genetic profiles from the most challenging samples. These amplification chemistries incorporate enhancements to the amplification buffer and/or introduce optimized thermal cycling parameters to specifically overcome the challenges presented by inhibited and low level samples. Developmental studies on hematin and humic acid models of inhibition demonstrate a clear improvement in the ability to amplify samples containing high amounts of inhibitors. Data generated from comparison of enhanced kits to previous STR amplification kits clearly demonstrates the increased recovery of genetic information with a greater number of interpretable alleles detected. This improved performance has been demonstrated in the laboratory on actual property crime sample types, particularly touch evidence.
DNA typing on touch evidence is based on the assumption that an individual who merely wears, handles, or touches an item will deposit their DNA, and that such contact can be used to develop a DNA profile of the responsible perpetrator. Items commonly swabbed for touch DNA include, steering wheels, ligatures, guns, door knobs, and other suspected points of entry. Historically, laboratories that process touch evidence samples have incurred a variety of stochastic and interpretational challenges due to inhibition and low template DNA, and the inability of traditional amplification kits to overcome these obstacles. Often, amplification of touch evidence has produced minimal, if any, probative information for criminal investigations, at a high cost to government agencies.
The introduction of high-performance amplification kits represents a potential solution to the challenges posed by touch and otherwise compromised forensic evidence samples. The efficacy of one enhanced amplification kit, the AmpFℓSTR® Identifiler® Plus kit, was recently evaluated by testing various challenged samples, a majority being touch evidence. In the kit evaluation, each sample amplified with the Identifiler® Plus chemistry was similarly amplified with a kit that has been long-established in forensic laboratories. In total, the enhanced chemistry captured 188% more allelic data than its predecessor, most likely due to the ability to overcome inhibition. Approximately 60% of the compromised samples failed to amplify with the traditional chemistry, while the enhanced kit was able to amplify each of the samples, producing profiles that were interpretable and often suitable for CODIS search. For example, biological material from a leather glove associated with an unsolved cold case crime from 1984 was successfully amplified with the enhanced kit during the evaluation, producing a complete male DNA profile for search in CODIS (Figure 3). The same DNA extract failed to amplify with the previous chemistry, most likely due to inhibition caused by tannins and other environmental insults.
Figure 3. DNA extracted from a leather glove analyzed with the Identifiler® kit (top) and the Identifiler® Plus kit (bottom).
An increase in the sensitivity, intracolor balance, and baseline quality was also observed, which further aided interpretation and deconvolution of the DNA profiles. The overall quality and magnitude of data recovered by the enhanced amplification kit represents great progress toward the resolution of criminal offenses that would otherwise remain unsolved.
Touch evidence samples frequently consist of mixtures of DNA from one or more contributors necessitating the interpretation of a mixed DNA profile. Interpretation of mixtures relies on parameters such as the heterozygote peak height balance, intracolor balance, and mixture proportion to enable a conclusion regarding the individual contributors to a mixture. In general, heterozygote peak height and intracolor balance are highest for higher input amounts of single source DNA. In the presence of inhibitors, certain loci may be more affected than others, resulting in a decrease in balance due to a lower effective amount of amplifiable DNA. Because the enhanced kits demonstrate a high resistance to the effects of inhibition, this problem is minimized.
Prior to the regular collection of DNA in crime scene processing many factors played a role in its limited use. Regrettably, costs were, and remain today, a major concern. From an analytical perspective,most governmental DNA forensic laboratories are limited as to how much casework they can accept. They are tremendously understaffed and lack adequate work and storage space. Some have as few as one or two forensic scientists to analyze hundreds of cases. Law enforcement also faces many issues such as proper evidence collection training and the proper complement of detectives/investigators for immediate follow up and arrest. There are judicial and correctional facility resource concerns as well; additional prosecutors and defenders, correctional personnel, and additional adequate housing for those convicted.
This begs the question, at what cost does a community sacrifice citizen safety and an overall reduction in crime? Community officials must balance the cost for expanding DNA analysis for all crimes versus the savings that is directly achieved though the reduction of overall crime and future crime.
Presently, in New York City, the New York City Police Department and the Office of the Chief Medical Examiner are working together to keep New Yorkers safe. New York City’s crime rate remains at record lows. The NYPD forensically investigates all applicable crime scenes and submits recovered DNA evidence to the OCME’s Biological Laboratory on a daily basis. In February 2007 the OCME’s Office opened a new state-of-the art Biological-DNA laboratory. They are now equipped and have all the required resources to analyze all DNA cases in a timely manner.
Careful attention to sample collection and improved extraction methods coupled with implementation of enhanced amplification systems capable of providing a maximum amount of information from challenging samples will greatly benefit laboratories seeking to achieve high first pass success rates for property crime samples.
As more jurisdictions expand their testing capacity to include property crimes, it is important to preserve a high quality system that maintains the integrity of the sample, while allowing for a significant number of additional tests. It is imperative the law enforcement and scientific communities work together to optimize the processes that benefit their communities as a new era of testing and investigative methods begins.
Joseph Blozis is a retired NYPD Detective Sergeant who served for 28 years, 22 of which he was assigned to the Forensic Investigations Division- Crime Scene Unit. Sergeant Blozis supervised over 2,500 crime scenes and coordinated unit training, including DNA collection. As coordinator for the NYPD’s Biotracks DNA program, he utilized his crime scene expertise to train field personnel in the recognition, detection, documentation, and recovery of DNA evidence at crime scenes.
Lynne Burley received a BS in Microbiology from the University of Illinois and an MS in Forensic Science from Michigan State University. She has been working at the Santa Clara County Crime Laboratory for the past ten years and currently serves as the DNA Technical Leader and a Supervising Criminalist.
Lisa Calandro is Director of the Forensic Science Applications Group in the Human Identification Group at Life Technologies. In her role, Lisa leads a team of Forensic Scientists to define user requirements for new human identity products and provide training and support to Life Technologies customers. She can be reached at firstname.lastname@example.org.
Lisa Lane Schade works with forensic DNA laboratories around the world to help define and execute the strategic direction for the Human Identification business at Life Technologies. Ms. Schade has a BS in Microbiology, a minor in Chemistry and a Master’s Degree from the University of Oklahoma. She can be reached at email@example.com.