Police do not get a second chance to collect evidence at a chaotic crime scene. On arrival, they must secure the site and immediately begin the meticulous process of inspecting, gathering, and recording all available evidence. It is a thorough job that requires precise attention to detail. Quite often, the success of a criminal investigation depends on collection and analysis of tiny items known as trace evidence. There are many challenges in achieving effective management of trace evidence. What is trace evidence? Generally, it is anything not routinely examined by other evidence units—DNA, firearms/toolmarks, drug chemistry, latent prints, etc. Examples are fibers, hair, glass, unknown powders, paint, explosives, plant materials, and vehicle filaments. An immediate question raised is: “How long does it take to train an examiner to perform all these tasks?”
For some functions in a crime laboratory, such as drug chemistry, analysts are well prepared from college to perform the analyses. Despite years of chemistry and instrumental coursework, a trace examiner will need further extensive training specific to trace evidence, especially in handling microscopic particles. The training answer depends on how many areas in which the examiner plans to subspecialize. It can take years to be competent in just a few types of evidence.
Challenges of trace evidence cases
Examiners have to master more than just instruments and particle manipulation. For instance, they need courtroom testimony skills and must be able to present scientific findings to help lay jurors understand what the evidence means to the case. They also must be aware that what they say might not be permitted in the courtroom. More than one mistrial has resulted from an analyst not being informed about rules applying to testimony. To be considered an expert, examiners need to be truly knowledgeable in the industries associated with evidence they examine.
If an examiner concludes that glass particles recovered from the suspect’s shoes “match” the glass from a broken window at the victim’s home, what does that mean? Is all glass the same? Is windshield glass different from window panes in a home? How different are they? These questions cannot be answered without a thorough understanding of the glass industry. What would it take to thoroughly understand the entire industry behind production of car paint, carpet and clothing fibers, explosives, vehicle head- and taillights, etc.?
Another challenge is that trace evidence cases are very tedious and time consuming. A typical drug chemist may work 75–125 cases per month, but a trace evidence examiner may handle only 6–10, depending on complexity. If the prosecution must prove a vehicle’s headlights were on or off at the time of an accident, the analysis might take a half day. A paint or fiber case could take a week or more. Fiber cases can be exceptionally time-consuming because the examiner has to “find” the evidence.
Consider a scenario in which a murder victim is found in bed. How do we find the fiber evidence? Naturally, the sheets, blanket, and pillowcases are composed of fibers and so are the nightclothes. Also, the victim may have worn different nightclothes since the bedding was last washed. The bedding, when washed, probably was placed in a dryer with other garments and household cloth items. So which of those microscopic particles may have come from the perpetrator?
Because trace evidence is so diverse, the laboratory needs sophisticated equipment, such as stereo-, polarized light, and comparison microscopes; microspectrophotometers; scanning electron microscopes; X-ray fluorescence; glass refractive index measuring instruments; gas chromatograph/mass spectrometers; Fourier transform infrared spectrometers; and many more. These instruments are expensive and generally require service contracts for maintenance and repair.
As noted earlier, informing the jury about the significance of a “match” or “exclusion” requires industry knowledge, and a common issue with trace evidence testimony is that the examiner cannot state a statistical probability. In the past quarter century, DNA has become the hallmark of forensic examinations. Once an individual is linked with a DNA sample, the expert witness can quantify the probability that another human could have the same DNA profile.
For example, suppose semen is identified on a victim’s bed and matched to John Doe. A statistical calculation can be performed to determine the odds that someone else might be the source of the seminal fluid. The data are compelling and infer the specimen came from a certain individual and no one else, unless there is an identical twin. Unfortunately, prosecutors and detectives are so reliant on this “slamdunk” evidence that they have, over the years, significantly devalued trace evidence examinations. As a result, the number of trace cases submitted to laboratories for analysis has steadily declined.
Since trace evidence units require sophisticated and costly laboratory instruments and highly trained examiners to work relatively few cases for which they generally are unable to generate statistical data, many law enforcement agencies throughout the United States are shutting down their trace evidence units. The benefits of DNA evidence and its statistical probabilities are obvious, but not every case has DNA evidence. In a hit-and-run, the victim could bounce off the car before shedding blood and DNA evidence. In these cases, the analysis of transferred paint evidence may inform police about the year, make, and model of the suspected vehicle.
Given the pressures faced by trace evidence units today, it is critical to utilize any technology that can help analysts with data entry, documentation, and quality control. A state-of-the art laboratory information management system can be a valuable tool that allows analysts to work more efficiently.
By storing information electronically, there is no need to rekey information. Basic case information, such as suspect and victim names, lab number, agency case number, points of contact, etc., are entered once and become available throughout the system. This prevents transcription errors. Instrument integration is a huge time-saver and quality assurance feature. Data can be parsed automatically into predefined fields or worksheets, enabling analysts to concentrate on data interpretation more than data entry. All data, case notes, property receipts, submittal forms, etc., are stored electronically and available with the click of mouse, saving labor chasing misfiled paperwork. Also, preparing analytical reports is much faster when selected data are prepopulated onto the report, and commonly used phrases can be easily inserted to minimize keystrokes.
Quality assurance and ASCLD-Lab/ISO 17025 compliance is critical in all units of the laboratory. A key feature offered by STARLiMS (Hollywood, FL) is a certified ASCLD-LAB technical assessor, which ensures the product has rigorous quality assurance features built into the core.
Analysts with heavy caseloads sometimes have difficulty remembering everything they must document for their analysis. Not only is it important to find trace evidence at the crime scene, it has to be documented and inventoried properly. An optimal LIMS should prompt analysts when they need to identify equipment used, perform QA checks on instruments, test reagents, review reports, etc. Standard operating procedures should be integrated so that analysts can skip checking a binder for information. QA managers will find the job much easier if their LIMS allows them to document all QA activities.
Much of the analytical work performed in a trace evidence unit involves comparing a known to an unknown, such as associating fibers collected from a suspect’s shoe to those in the carpeting inside the victim’s home. For this type of examination, the LIMS should provide a cross-tab view of the data to enable analysts to evaluate the characteristics of both items side by side for quick and accurate comparisons.
Also, the laboratory should be able to define its own worksheets and allow analysts to populate the same forms used in the paper-based system. For example, STARLiMS users can prepopulate results where appropriate into drop-down and multiselect menus. This also helps secure data integrity by defining how some data are entered. In addition, the electronic signature of a second analyst can be captured when verification of an analytical result is necessary. If mathematical calculations are needed, they can be defined within the system to ensure accuracy and free the analysts from performing manual calculations.
LIMS can be a valuable tool that allows crime laboratories to streamline evidence documentation and management. STARLiMS provides a multidisciplinary LIMS solution that provides out-of-the-box functionality that can be configured to meet the needs of working forensic laboratories. The STARLiMS forensic package addresses all aspects of forensic investigations, including crime scene, property management, laboratory, quality assurance, document management, and medical examiner functionality.
Trace evidence is one of the most intriguing units in the crime laboratory. Despite the challenges, laboratories must endeavor to keep their trace units open so that these valuable skills are not lost from the crime-fighting toolbox forever.
Robin Gall, Ph.D., PMP, is Senior Product Manager, Forensics, STARLiMS Corp., 4000 Hollywood Blvd., Ste. 333 South, Hollywood, FL 33021-6755, U.S.A.; tel.: 954-964-8663; fax: 954-964-8113; e-mail: firstname.lastname@example.org. The author is also a certified ASCLDLAB/ ISO 17025 technical advisor.