Using DNA to Fight Property Crime
Written by Joseph Blozis   

DNA is a very powerful law enforcement tool and is often referred to as the “finger-print of the 21st century.” Less than ten years ago in major cities such as New York, crime scene investigators recovered DNA only in high-profile violent felonies that were associated primarily 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 that included residential and commercial burglaries—were routinely processed forensically only for the presence of latent and patent fingerprints.

DNA Property Crime Forensic Laboratory Analysis Evidence Crime Scene New York City Police Department


In September 2003, New York City Police Department (NYPD) implemented a pilot program entitled “Biotracks” to solve no-suspect burglary cases. The program was funded by the President’s DNA Initiative Program and was administered through the National Institute of Justice (NIJ), together with the New York State’s Division of Criminal Justice Services. The NYPD recovered the DNA evidence from no-suspect burglary scenes in northern Queens, 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 (OCME) Biological Laboratory for technical review. The OCME would then upload applicable DNA profiles to the Combined DNA Identification System (CODIS). Results—including matches—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.

In September 2005, the Biotracks program was expanded throughout New York City, and proved to be a tremendous success. More than 3,430 crime scenes were processed in which 6,391 items of DNA-related evidence were recovered. As of April 2008, when the program concluded and stopped tracking statistics, 1,558 CODIS-eligible profiles had been generated, resulting in 692 case-to-offender matches involving 548 offenders, and these statistics are expected to dramatically increase over time. The vast majority of offenders pled guilty and received lengthy incarceration. The program revealed that many of the offenders were recidivists whose arrest records indicated that the crime of burglary was a common denominator and that burglary was a stepping-stone to more serious crime. The Biotracks program became a model for how all crime scenes are now processed.

Today, the NYPD forensically investigates all applicable crime scenes (including homicides, sexual assaults, robberies, property crimes, gun possession, and auto theft) and submits recovered DNA evidence to the OCME’s Biological Laboratory on a daily basis. New York City’s crime rate remains at record lows.

The proven success of programs like Biotracks in New York City and other jurisdictions have helped make the case to expand the regular use of DNA in crime scene processing. However, many law enforcement agencies continue to face significant implementation challenges.

Regrettably, cost is still a major concern. From an analytical perspective, most governmental forensic DNA laboratories are limited in how much casework they can accept. They are tremendously understaffed and lack adequate work and storage space. Some have only one or two forensic scientists to analyze hundreds of cases. Agencies also face issues such as proper evidence-collection training and the proper complement of detective investigators for immediate follow-up and arrest. There are judicial and correctional facility concerns as well, including the need for additional prosecutors and defenders, correctional personnel, and adequate housing for those convicted.

Indeed, the need for additional resources can seem daunting. However, the cost of inaction is much greater, sacrificing the safety of law-abiding citizens and the long-term savings that can result from an overall reduction in crime. It is important that community officials avoid short-term tunnel vision on costs and instead embrace a longer-term vision for potential savings. It has been shown that DNA analysis not only solves crimes but reduces future crime. For example, the city of Denver, Colorado
—part of the NIJ’s 2008 Urban Institute Report—and Palm Bay, Florida have proven that the use of DNA in property crimes results in significant crime reduction that ultimately saves millions in taxpayer dollars.

A Practical Guide to Crime Scene Processing

DNA Property Crime Forensic Laboratory Analysis Evidence Crime Scene New York City Police DepartmentCrime scene processing normally starts with the initial 911 call. It is then followed by the first responders’ actions at the crime scene. First responders must be cognizant of their own safety upon arriving to the scene, and should be fully trained to quickly assess and evaluate what actions must be taken. Initial actions may be to confront a suspect, render aid to a victim, search for a suspect, interview a complainant, determine what people are considered witnesses, and make provisions to separate them. First responders should also be prepared to request additional assistance, determine if there are multiple crime scenes, make command notifications, take copious notes, prepare detailed reports, and safeguard and preserve the scene. All of this must be done in an expeditious manner while maintaining the integrity of the scene.

Preserved scenes must keep unauthorized persons out—including police personnel. After the crime scene has been established, the only official personnel that are permitted into the crime scene are crime scene detectives, medical personnel, medical examiners, district attorneys, detective supervisors, and assigned detectives. A safeguarding officer should maintain a log of all responding officers who were at the scene, including those who had left. DNA elimination samples of those who were at the scene are as important as the recovered unknown DNA samples.

Personal Protective Equipment

Crime scene investigators must don personal protective equipment (PPE) prior to initial entry and throughout the entire processing of the scene.

PPE is essential to prevent contamination. It consists of a full Tyvek suit, including a hood, booties, face mask, and gloves. (Some law enforcement agencies do not use full-body protection, but at a minimum gloves and a mask are a must.) DNA evidence becomes contaminated when DNA from another source is mixed in with DNA relevant to the case. There are also serious health and safety concerns associated with touching biological evidence. For these reasons, crime scene investigators and laboratory personnel should always wear PPE, use clean instruments, and avoid touching other objects (including their own bodies) when handling evidence or the items used to collect evidence. To prevent contamination of the samples, it is imperative that crime scene investigators change their disposable gloves between each sample collection.

Establish a Forensic Tactical Plan

Crime scene investigators must establish a forensic tactical plan on how to approach, evaluate, and process the scene. It is recommended that they confer with first responders, investigators, and victims. They should establish a singular entry and exit path and perform a scene walk-through. At this time, they should determine a sequence for the collection of forensic evidence.

Crime Scene Documentation

Documentation of the crime scene will consist of photographs, notes, sketches and measurements.

  1. Photograph the item in place, showing how it looked before collection.
  2. Take written notes, describing the condition of the evidence, what was collected, and how it was collected.
  3. Take measurements, showing the location of the evidence and its position relative to other objects.
  4. Sketch the location of the evidence in the crime scene sketch.

DNA Evidence Supplies

Having the proper supplies on the scene—and knowing how to use them—is critical to the collection of usable DNA samples. A crime scene investigator’s tool kit 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 applicators (swabs), used to collect samples.
  • Hydration, used to moisten the swab. Note: Distilled water is good; sterile water is better; and phosphate saline solution is the best.
  • Plastic pipettes, used for transferring the distilled water to the swabs.

There are many types of swabs that can be used effectively, including those with traditional cotton-fiber tips as well as foam and flocked substrates. Flocked swabs, such as the 4N6FLOQSwabs (from Life Technologies) offer notable advantages, mainly due to their design with short perpendicular nylon microfibers that act like a soft brush to facilitate improved collection of cellular material. Unlike traditional fiber wound swabs, flocked swabs have no internal absorbent core to disperse and entrap the specimen; therefore, the sample stays close to the surface for faster and more efficient laboratory processing.

Swabbing Techniques for Touch DNA

  1. DNA Property Crime Forensic Laboratory Analysis Evidence Crime Scene SwabbingDon personal protective equipment.
  2. Withdraw distilled water from the vial with a sterile plastic pipette.
  3. Remove a sterile swab from the sealed container. (Use each swab only once.)
  4. Place one drop of distilled water on the side of the swab tip.
  • Avoid saturating the swab.
  • Avoid dipping the swab into the distilled water.
  1. Swab the area.
  • Rotate the swab so the entire surface of the swab is used.
  • Avoid re-using areas of the swab if possible (re-use may re-deposit samples onto the substrate).
  • Maximize swab coverage:
    • One swab for every 15 square centimeters of surface area.
    • Use additional swabs as necessary.
    • Label the swabs accordingly.

Note: When swabbing an irregular, grainy surface,

  • Swab with the grain;
  • Swab back and forth, rotating the swab surface to ensure that the same area is not re-used.
  1. Re-swab the area with a dry, sterile swab.
  2. Air-dry the swabs.
  3. Place the swabs into the same paper enclosure.

Collection from Stains and Other Biological Sources

  1. Collect the stain using the moistened portion of the swab. There is a correct and incorrect way to moisten a swab. For example:
  • Proper swab saturation involves only a small amount of water, swabs dry quickly, and, as a result, samples are concentrated.
  • Improper swab saturation involves too much water, resulting in slow-drying swabs and diluted samples.
  1. Use multiple swabs, if necessary, to collect the entire stain.
  2. Re-swab area with a dry sterile swab
  3. Air-dry all swabs
  4. Place all swabs into the same paper enclosure

Biological evidence such as skin tissue, bone fragments, teeth, and nails have a high likelihood of yielding a full DNA profile. These items must be packaged in paper or cardboard and sent to the laboratory for DNA profiling. They should not be processed in the field.

Prior to recovering a blood sample from glass or other substrates, use a magnifying glass to examine the blood for the presence of ridge detail. Ridge detail in a blood sample indicates a patent fingerprint that must be processed accordingly. If at all possible, collect the entire substrate that the bloody patent print is on, package it, and forward the entire item to the laboratory. If the substrate cannot be packaged and sent to the laboratory, photograph the print thoroughly with a scale in place. Then proceed with the swabbing process.

Swabbing is not the only way to collect evidence for DNA analysis. Additional DNA collection methods include:

  • Scraping dried biological evidence;
  • Cutting a swatch from the substrate that contains the unknown stain;
  • Submitting the entire substrate to the laboratory.

Dried biological samples on substrates other than clothing can be scraped with a sterile scalpel and collected. The scrapings are then placed in filter paper, folded, and inserted into a paper envelope. Scalpel blades must be sterilized or replaced after each DNA sample is recovered. In addition, it is much easier and safer to swab a sample than to scrape a sample and possibly cut yourself. Confer with the laboratory personnel and establish a protocol to determine the preferred collection method.

Submitting the entire substrate to the laboratory can often be advantageous. In the event that the DNA results are inconclusive or the quantity is insufficient for a full DNA profile, the evidence is easily accessible for re-processing. Processing a substrate at the crime scene eliminates the opportunity for a second analysis. When it is not practical to submit the entire substrate, a swatch can be cut and submitted instead.

Clothing should not be processed at the crime scene. Instead, it should be documented, packaged and submitted to the laboratory. Clothing must be examined for stains, hair, skin cells, and other trace materials—and a laboratory environment is much more appropriate than a crime scene for such a complex examination.

Fingerprints and Touch DNA

Touch DNA exists where a suspect has touched a surface at the crime scene, possibly leaving a fingerprint as well as DNA. Therefore, before the scene can be processed, it must be decided whether the scene will be processed for DNA, fingerprints, or both. Areas that are smooth, hard, and non-porous should be processed for fingerprints. Areas that have irregular surfaces should be processed for DNA. Before swabbing an area for DNA, make sure the area is not conducive for fingerprints, since you may be swabbing through a latent fingerprint.

When evaluating a fingerprint, use a magnifying glass to determine if there is a sufficient amount of ridge detail to recover the print. When there is an insufficient amount of ridge detail or the fingerprint is clearly a smudge, consider processing it for DNA. It is also possible to recover DNA from areas that have already been processed for fingerprints by swabbing the area after the fingerprint is lifted. However, be mindful of contamination issues concerning the fingerprint brush. A fingerprint brush that has been used at other crime scenes has the potential of containing DNA from those scenes and being transferred to surfaces at the present crime scene.

Substrates such as drinking glasses can be processed for both DNA and fingerprints. First, process the rim area for DNA; then, process the entire glass for fingerprints. Other small substrates that have minute surface areas should be processed for DNA.

Probative and Non-Probative Evidence

Evidence collectors are not garbage collectors, and the crime laboratory should not be treated as a garbage dump. Garbage in leads to garbage out. Evidence collectors must be thoroughly trained to process a scene and 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 that would be 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 an investigatory lead or at a later date prove significant to the investigation.

Crime scene investigators must be trained in the recognition and collection of probative evidence as the first priority, and the ability to differentiate the probative from the non-probative evidence. This is essential to prevent crime laboratories from becoming over-burdened with non-probative evidence.

Types of DNA Samples

There are three categories of DNA samples:

  • Crime scene samples are the unknown forensic DNA samples that are recovered at crime scenes. An evidence collector recovers the sample, but (as with fingerprints) does not know who deposited the sample. Crime scene samples are profiled and compared to suspect profiles or searched in the DNA database against other crime scene samples and offenders.
  • Elimination samples are samples from individuals such as victims or victims’ family members who had prior legal access to the crime scene. Elimination samples should include evidence collectors and laboratory personnel. Elimination samples are also referred to as known samples, reference samples, or buccal swabs. Buccal swabs are elimination samples that are obtained by swabbing the interior of an individual’s mouth. They are used for comparison purposes during DNA analysis to eliminate known DNA profiles from those recovered from the crime scene.
  • Abandoned samples are DNA samples that are abandoned in a public area by an individual known to law enforcement. It could be as simple as an individual discarding a cigarette butt in a public domain.

Transporting and Storing DNA Evidence

DNA evidence should be transported to the laboratory as soon as possible. Once the processing of the crime scene has concluded, place all of the sealed individual packages of DNA evidence into one carrying box or bag. Make sure that all of the evidence is accounted for. Place the box into a vehicle and transport the evidence to the laboratory without delay. Keep the evidence cool and dry. Transport liquid samples in refrigerated or insulated containers.

Extended exposure to heat or humidity causes degradation of biological evidence. To reduce this threat, move the packaged items from the crime scene to a suitable storage facility as soon as possible.

Degradation is the breaking down of DNA into smaller fragments by chemical or physical processes. Degradation of DNA may limit its use as evidence. Factors that promote DNA degradation include:

  • Ultraviolet rays (prolonged exposure);
  • Heat, humidity, and moisture;
  • Bacteria and fungi (often found in foliage and soil); and
  • Acids or chemical cleaning solutions (such as bleach).

Actions such as storing evidence in vehicle trunks, vans, office desks, direct sunlight, frost-free refrigerators, and non-temperature/humidity-controlled facilities subject the biological evidence to increased heat, humidity fluctuations, and ultraviolet rays—all factors that can accelerate degradation.

If someone other than the investigator is transporting the evidence, chain of custody must be transferred. It is transferred again when the evidence reaches the laboratory.

The storage of DNA evidence is the last link in the chain of custody. Whether DNA evidence is stored in the laboratory or in a storage facility, certain conditions must be adhered to in order to prevent degradation. DNA evidence should be stored in a spacious, cool, and dry environment. Although it is preferred, most DNA evidence does not require refrigeration and may be stored at ambient room temperature or cooler.

About the Author

Joseph Blozis is a retired NYPD Detective Sergeant who served the City of New York for 29 years, including 22 years in the NYPD’s Forensic Investigations Division’s Crime Scene Unit and Police Crime Laboratory. He is presently a contracted consultant providing services for federal agencies and global DNA companies. He is an instructor, lecturer, and subject-matter expert who has developed training curriculum for the United States Department of State’s Antiterrorism Assistance Program for Terror Related Crime Scene Investigations and is the lead instructor for the International Association of Chiefs of Police (IACP) Comprehensive Crime Scene Course.

Additional Reading

Roman, J.K., S. Reid, J. Reid, A. Chalfin, W. Adams, and C. Knight, The DNA Field Experiment: Cost-Effectiveness Analysis of the Use of DNA in the Investigation of High-Volume Crimes, final report submitted to the National Institute of Justice, U.S. Department of Justice, Washington, DC: April 2008 (NCJ 222318). This report is available here.

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