Introducción a la criminalísticas y a las ciencias forenses

A criminalist (aka crime scene technician, examiner, or investigator) is a person who searches for, collects, and preserves physical evidence in the investigation of crime and suspected criminals [see job description]. They typically work in city or regional crime labs and are expected to do more than the forensic scientists and crime lab technicians there. They are expected to be on call 24 hours a day to go out to crime scenes, frankly when and where detectives are stumped. Some jurisdictions require the presence of a criminalist at all major crime scenes. The services of a criminalist are used at the beginning of a case. By contrast, the services of a forensic scientist are primarily used at the end, or courtroom testimony phase, of a case. All crime lab employees must be ready to offer expert testimony in court, however. Criminalists usually get called to testify about matters of contamination, cross-contamination, and chain of custody, but many of them (senior criminalists) have developed an interpretive expertise, for example, in blood spatter analysis, trace evidence, impression evidence, or drug identification, as well as skills at crime reconstruction and sometimes profiling (Levinson & Almog 1989).
The term criminalistics (Kriminalistik) was first used by Hans Gross in 1891, but the term was mostly forgotten until the 1960s when a series of cooperative movements took place between police agencies and criminal justice or criminology departments to establish criminalistics (Univ. of California) and forensic science (Michigan State) college programs. Professors Paul Kirk in California and Ralph Turner in Michigan (among many others) were pioneers in those movements. As Osterburg and Ward (2000) imply, criminalistics programs (available at forty-one community colleges and only one four-year college) followed the police science model to record, identify, and interpret the minutia (minute details) of physical evidence, and forensic science (available at fourteen four-year colleges and nine master’s degree programs) followed the medical science model to apply generally accepted principles of established disciplines (like pathology, serology, toxicology, odontology, and psychiatry) to the scientific examination of physical evidence. Forensic science is the broader term because criminalistics is a branch of forensic science. «Forensic» is simply an adjective that can be put in front of any science applied to answering legal questions. The American Academy of Forensic Sciences web site highlights about twenty various degree programs that relate to some aspect of criminalistics or forensic science education.
The world’s first crime laboratory was established by Edmond Locard in Lyon, France during 1910. The famous Locard Exchange Principle that «every contact leaves a trace» is named for him, after Locard solved a strangling case by using fingernail scrapings. In America, a few major cities and the FBI obtained crime labs during the 1930s, and by the mid-1970’s (the birth of criminal justice), 47 states had crime labs. A few criminal justice programs that existed prior to the explosion of the field in 1974 offered a criminalistics or forensic science concentration, but today, most criminal justice programs only have one course in criminal investigation. Post-1975, the criminal justice model became an attempt to make sense of whole systems of justice, and the criminology model, dominated heavily by sociology until about 1990, became theory, research, and policy-driven. Many criminalists consider themselves (professional) criminologists, but few criminologists consider themselves criminalists.
With federal police agencies, two (2) organizations stand out above the rest, the FBI and ATF, mainly because their crime labs are pretty much considered the tops in the field and a model for elsewhere.
FBI crime lab:
4 sections: (1) Scientific analysis (DNA, Firearms-toolmarks, Hairs and Fibers, Materials Analysis, Chemistry and Toxicology, Questioned Documents; (2) Special Projects (film, photography, composites, art, computer design); (3) Fingerprinting (some 200 million records); (4) Investigative Operations and Support (grew out of Questioned Documents unit and includes lie detection of various sorts). The FBI lab only handles violent crime, works exclusively for the prosecution, and is considered the world’s largest lab.
ATF crime lab:
Handles (1) Explosives, bombs, arsons (and does it well); (2) Trace evidence and deciphering firearms ownership and usage; (3) Disaster response teams (kind of like FEMA); (4) Field support; and (5) some Gang intelligence record keeping. ATF labs are typically very high-tech and have always been accredited.
It’s typical for a Crime Lab to have 4 divisions under a Director’s Office: (1) a section dealing with anything pertaining to fluids, this being called a Serology Division; (2) a section dealing with unknown substances, drugs, or poisons, this being called a Chemistry or Toxicology Division; (3) a section dealing with anything so small, like hairs or fibers, that they need to be looked at under a microscope, this being called a Trace Evidence, Biology, or Microscopy Division; and (4) a section dealing with guns, weapons, instrumentation, or whatever, this being called a Ballistics, Firearms, or Fingerprinting (Dusting and Lifting) Division (where Interns usually work).
There are about 350 crime laboratories in the U.S. and at least 80% of them are affiliated with a police agency (where they typically hold bureau status in the organization). The rest are located in the private sector and some of these are exemplary and known for a particular specialty: Cellmark Diagnostics (for DNA), Battelle Corp. (for arson cases), and Sirchie Corp. (for fingerprinting and trace evidence collection), to name a few. There is a shortage of DNA laboratories since only 120 labs are set up to do DNA testing (Steadman 2002). Almost all labs in existence are forensic labs, where «forensic» means the experts there are available to give courtroom opinions, but when a lab is set up to receive evidence from ongoing criminal investigations, this is called casework, and the lab is referred to as a casework lab.
You can’t just start up a crime lab anywhere or anytime you feel like it. Things are set up geographically so that ON AVERAGE, A LAB IS ALMOST ALWAYS 50 MILES WITHIN 90% OF THE POLICE AGENCIES. There’s some places that buck this pattern, but usually each state has one «parent» lab and 5-6 regional labs. They are always hiring and looking for help, as there’s a labor shortage of qualified applicants. There’s also usually a work backlog, and some labs and state systems are so backed up, that it takes many months to get the results back on an evidence analysis. But in all fairness, the backlog situation should not be a concern because crime labs were never intended to replace a field investigation. The point of this is that police investigators should never come to rely on a crime lab, but use it as a supplement to their own investigative skills. Criminalistics and forensic science are not silver bullets.
CHAIN OF CUSTODY: There are many sources of error. Evidence has to be discovered (police or criminalist), it has to be collected (police, crime scene technician, or criminalist), and then it has to be packaged, labeled, and transported (police supervisor or criminalist). Once it gets to the lab, it has to be logged in, assigned an identification number, placed in storage, kept from intermingling with other evidence, and analyzed (criminalist, crime lab technician, or forensic scientist).
Before any laboratory work is done, it must be ensured that the workplace is clean and contamination free. Then, the evidence is visually inspected and properly described to document its condition. Often, it will be photographed, weighed, and sketched. Then, the laboratory worker (criminalist, crime lab technician, or forensic scientist) will have to figure out what tests are appropriate, if sufficient amounts of the evidence exist, properly dissect the portion to be tested, and properly prepare the testing material (which might include the delicate mixing of numerous chemical compounds), all the while continuing to document each step. Only then does any testing begin.
Some tests include as many as five or six separate procedures, each of which must be properly performed and documented, the evidence properly repackaged and relabeled, and once again transported to storage. Only then does the lab worker engage in the process of interpreting what the experiments have disclosed. A report is prepared and the contents of that report must be precisely correct.
At the prosecutor’s discretion, the evidence has to make it back to the police evidence room, where it will be stored until he/she decides they want to use it or want more testing performed, in which case it goes back to the crime lab. It should be fairly evident that all this transportation of evidence gives rise to numerous possibilities for error in the form of destruction, mishandling, and contamination.
INTEGRITY: It’s important a crime lab find some system for establishing its credentials as a forensic laboratory. A couple of the organizations that perform this function include the American Society of Crime Laboratory Directors (ASCLD), the National Forensic Science Technology Center (NSFTC), and the College of American Pathologists (CAP). In addition, labs that specialize may also apply for credentials from an organization, or Board, which regulates that specialty. For example a lab that performs odontological work might apply to the National Board of Forensic Odontology.
Generally, whenever a lab applies for accreditation, it has to meet certain minimum requirements which include, among other things, the development and publication of: 1) a Quality Control Manual, 2) a Quality Assurance Manual, 3) a Lab Testing Protocol, and 4) a program for proficiency testing. Quality control refers to measures that are taken to ensure that the product, for example a DNA-typing result and its interpretation, meets a specified standard of quality. Quality assurance refers to measures that are taken by a laboratory to monitor, verify, and document its performance. A basic business principle is that QA serves as a check on QC. Protocols consist of a few hundred pages of highly technical manuals and should include such things as «validation studies» which the lab performed itself to make it capable of performing tests in any particular discipline.
Proficiency testing determines if the lab workers individually, and the laboratories as institutions, are performing up to the standards of the profession. In these tests, samples to be examined are given to a laboratory or particular worker, but the results are already known by a test giver. There are two methods employed in administering these tests, blind and known. In the blind test, the lab worker doesn’t know that a test is taking place; they think the evidence sample they are working on is just another case. The open proficiency test is like an open book exam. In addition, individual lab workers join associations to beef up their resumes. The two main ones are the American Academy of Forensic Sciences (AAFS), the American Board of Criminalistics (ABC).
In general, attacks on laboratory expertise come in three categories (which are the same techniques for attacking physical evidence): (1) Tampering, (2) Contamination, and (3) Substitution. Tampering refers to allegations that the crime scene or piece of evidence was tampered with. There’s a presumption of regularity on the side of the prosecution, so this is hard to prove. Contamination is somewhat easier to allege, given irregularities in the chain of custody. Substitution (or mistake) is a problem if the lab workers are new, inexperienced, or lack the appropriate credentials.
Physical evidence is part of the «holy trinity» for solving crimes — physical evidence, witnesses, and confessions. Without one of the first two, there is little chance of even finding a suspect. In homicide and sexual assault cases, physical evidence is the number one determinant of guilt or innocence. Physical evidence is also the number one provider of extraordinary clearances, where police can link different offenses at different times and places with the same offender. Working with physical evidence means being aware at all times of what the prosecutor needs to win the case in court. This means knowing the Types of Evidence and the Laws of Evidence.
There are 4 types of Evidence:
Testimonial — this is the kind of evidence that comes to court through witnesses speaking under oath or affirmation. They could be testifying about something they saw (eyewitnesses), something they heard (hearsay witnesses), or something they know (character, habit, or custom witnesses)
Physical — these are tangible objects that are real (sometimes said to speak for themselves because they can be taken into the jury room), direct (no preliminary facts needed), and not circumstantial (do not require an inference to be made), although circumstantial evidence is sometimes offered and strengthened by expert testimony. Examples of physical evidence would include the gun used to commit the crime, trace particles found at the crime scene, property recovered, fingerprints, shoeprints, handwriting, etc.
Documentary — this is usually any kind of writing, sound or video recording. It may be the transcript of a telephone intercept. Authentication of the evidence is usually required along with expert testimony at times.
Demonstrative — these are types of real evidence used to illustrate, demonstrate, or recreate a tangible thing; for example, a cardboard model mockup of the crime scene or other constructed-to-scale models. The purpose of this stuff to to replace timely, expensive, and possibly prejudicial jury trips to the crime scene.
Both forensic scientists and criminalists need to be intimately familiar with the Standards of Admissibility for Scientific Expertise, since these vary from state to state, and sometimes even from court to court within states.
Relevancy test (FRE 401, 402, 403) – this is embodied in the Federal Rules of Evidence and state versions which essentially involve a liberal rule allowing anything that materially assists the trier of fact (jury) and is deemed relevant by the trier of law (judge).
Frye standard (Frye v. U.S. 1923) – for the results of a scientific technique to be admissible, the technique must be sufficiently established to have gained general acceptance in its particular field. This is the «general acceptance» test that often requires knowledge of the literature.
Coppolino standard (Coppolino v. State 1968) – the court allows a novel test or piece of new, sometimes controversial, science on a particular problem at hand if an adequate foundation can be laid even if the profession as a whole isn’t familiar with it.
Marx standard (People v. Marx 1975) – the court is satisfied that it did not have to sacrifice its common sense in understanding and evaluating the scientific expertise put before it. This is the «common sense» or «no scientific jargon» test, and it is rarely used.
Daubert standard (see Lecture on Daubert). This test requires special pretrial hearings for scientific evidence and special procedures on discovery. This is a rather stringent test that requires knowledge of Type I and Type II error rates, as well as validity and reliability coefficients.
Since criminalistics is the recording, identification, and interpretation of minutia (minute details), a number of standard techniques and procedures have been developed to do this. It is important to understand the basic concepts behind these techniques. A more useful term than minutia is striations, which are scratch marks caused by irregularities or lack of microfine smoothness, such as those found on fingerprints, bullets, cartridges, casings, or tool marks. With evidence like paint, hair, grease, and glass, the chemical composition (qualitative and quantitative) provides the details. With other types of evidence, such as glass fragments, the morphology (or form) of an object reveals valuable information, such as a jigsaw puzzle fit linking pieces of broken glass together.
Criminalists know how to operate a variety of devices and machines. The three simplest devices are lights, camera, and microscope. By adjusting the light on an object, the morphological and composition characteristics of evidence often become visible. A basic principle is contrast, as in when the background color of an object is made different than the foreground color. Cameras often allow the use of lens filters to screen out certain colors, and contrast (among other things) can be increased or decreased in photography. Microscopes are the main technique for enlarging resolution, although it is possible to enlarge without enhancing resolution. Most physical evidence reveals valuable detail at magnifications between 2x and 10x. The more complex devices are called analytical instruments, and consist of the following:
Spectrophotometers Organic/Inorganic Nondestructive Quantitative
Mass Spectrography Organic Destructive Qualitative
X-Ray Diffusion Crystalline Nondestructive Qualitative
Neutron Activation Inorganic Nondestructive Qualitative/Quantitative
Scanning Electron Organic/Inorganic Nondestructive Semi-quantitative
X-Ray Dispersion Inorganic Nondestructive Qualitative
Chromatography Organic Nondestructive Qualitative/Quantitative
There are many more organic substances than inorganic substances. Most drugs, explosives, hairs, and biological fluids are organic, based on the element carbon. Most dirt, gunpowder, poisons, paint, and glass are inorganic, although some substances represent a mix or organic and inorganic.
Without doubt, the most important concept in criminalistics is identification, or what Paul Kirk called individualization (Kirk 1936). Identification produces unequivocal (certain) interpretation. An equivocal crime scene, by comparison, yields physical evidence subject to different interpretation (and is the basis for crime reconstruction and profiling). When a number of details are put together (as in points of comparison), so that they constitute a class of one (by itself), they are said to establish an identity, also called individual characteristics, or entities in a class by itself. At this point, if there are similarities between evidence from the crime scene and evidence from a suspect, the expert can say, without a doubt, that identity has been individualized.
It is important to clearly understand the concepts of identity, match, class and individual characteristics. Identity is a set of characteristics (combinations of class characteristics or combinations of class and individual characteristics) by which a thing is recognizable or known. Identity is the same as pattern. A pattern is established, for example, when a particular piece of class evidence like fiber (for which there are large quantities in the population) is put together with another piece of class evidence like red hair (which usually only exists in the subpopulation of white people). It cannot be said the investigator has «individualized» anything at this point, but the red hair in this example can be considered enough of an individual characteristic which combines with the class characteristic to establish identity. At this point, if there is a «match» between the fibers and hair from the crime scene with a suspect, the examiner can say the crime scene (unknown or questioned) sample «may have come from the same source» as the suspect’s (known or exemplar) sample, which is sufficient for probable cause. Identity can also be used to conclusively eliminate people as suspects.
Class characteristics alone do not allow matches with a single suspect. Matches for evidence with individual characteristics do allow pinpointing a particular suspect. Matches at the individual level are called similarities, because in theory, there’s no such thing as a perfect match. An example of a similarity, or match in individual characteristics, would be a number of comparable points of comparison between the friction ridge lines on a latent (crime scene) fingerprint with the fingerprints of a particular suspect. This kind of (true) match allows the examiner to say that, because the similarities outweigh any dissimilarities, the crime scene (unknown or questioned) sample «did come from the same source» as the suspect’s (known or exemplar) sample, which is sufficient, most of time, for proof beyond a reasonable doubt.
Reliability and integrity are enhanced if the examiner has conducted tests on standards using controls. A standard is the opposite of exemplar. An exemplar always comes from a suspect or something representing a known modus operandi or signature. Standards consist of simultaneous tests done on items taken from the «background» or nearby the crime scene (control sample), items similar to one the suspect used, such as test firings of a similar weapon (standard sample), or items used for calibration purposes kept in stock at the lab (reference sample).
The astute student may notice that the word «match» is used a couple of different ways in criminalistics. Nobody uses the phrase (true) match, for example, like I have used in my explanations above. Some people prefer the term «matching» (Ramsland 2001). Abuse of the term «match» is even worse in forensic science, which allows different disciplines to set their own criteria and standards. To wrap things up, let’s conclude with an interesting topic — the points of comparison method — and then attempt to present a table which classifies evidence by their class and individual characteristics.
At one time around 1900, there was a system called the anthropometric system that had been invented by a Frenchman, Alphonse Bertillon (1853-1914), consisting of numerous, minute body measurements, such as finger and forearm lengths. This system was in competition with fingerprinting (technically called dactylography), discovered by Henry Faulds and popularized by Francis Galton. Bertillon based his system on the use of 11 points of comparison, calculating his odds of being wrong on any given match being 4 million to 1. These type of calculations form the basis of a number of forensic sciences relying upon the Points of Comparison method, such as odontology, firearms examination, and questioned document examination. Due to population growth since Bertillon’s time, the contemporary method is based on at least 12 points of comparison and an odds ratio of about 6 million to 1. An odds ratio or percent chance of being wrong also characterizes the quantitative information provided by modern analytical techniques such as spectrography, chromatography, and DNA typing (in the case of DNA, the odds ratio is an amazing 30 billion to 1).
There is no such thing as a comprehensive classification scheme for all types of physical evidence. Some types of class evidence can be somewhat individualized, such as hair and blood, and some individual types are best considered both class and individual evidence. With that having been said, here’s a table that lays out some basic distinctions:
American Academy of Forensic Sciences
American Board of Criminalistics
American Society of Crime Lab Directors
Association of Firearms and Tool Mark Examiners
ATF Laboratories Home Page
California Association of Criminalists
Canadian Society of Forensic Science
Consulting and Education in Forensic Science
FBI Lab’s Journal of Forensic Science Communication
Forensic Science Resources for a Criminal Fact Investigation
History of Forensic Science Timeline
International Association for Identification, California Division
Kruglick’s Forensic Science & Criminal Law Site
Kruglick’s Primer on Investigation of Forensic Evidence
The Microscope Mega-Site: Molecular Expressions
Why the Bertillon Anthropometric System Failed
Young Forensic Scientists Forum
Zeno’s Forensic Site
Brenner, J. (1999). Forensic Science Glossary. Boca Raton: CRC Press.
Capsambelis, C. (2002). «So Your Student Wants to be a Crime Scene Technician?» Journal of Criminal Justice Education 13(1): 113-27.
Conklin, B., D. Shortelle & R. Gardner. (2002). Encyclopedia of Forensic Science. NY: Oryx Press.
Fisher, B. (2000). Techniques of Crime Scene Investigation. Boca Raton: CRC Press.
Fridell, R. (2000). Solving Crimes: Pioneers of Forensic Science. NY: Grolier.
Gross, H. (1891) (1924). Criminal Investigation. translation from System Ker Kriminalistik. NY: Sweet & Maxwell.
Houde, J. (1999). Crime Labs: A Guide for Nonscientists. Ventura, CA: Calico Press.
Kirk, P. (1936). «The Ontogeny of Criminalistics.» Journal of Criminal Law, Criminology, and Police Science 54: 236-41.
Lee, H. & H. Harris. (2000). Physical Evidence in Forensic Science. Tucson: LJP Co.
Levinson, J. & J. Almog. (1989). «The Evidence Technician: An Israeli Approach.» Law & Order Magazine 37:48-50.
Osterburg, J. & R. Ward. (2000). Criminal Investigation. Cincinnati: Anderson.
Ramsland, K. (2001). The Forensic Science of C.S.I. NY: Berkley Boulevard Books.
Saferstein, R. (2000). Criminalistics (7e). Englewood Cliffs: Prentice Hall.
Steadman, G. (2002). Survey of DNA Crime Labs. BJS Bulletin, NCJ 191191.
Stoney, D. (1988). «A Medical Model for Criminalistics Education.» Journal of Forensic Sciences 33:1086-94.
Last updated: 01/06/04
Syllabus for JUS 315
Syllabus for JUS 425
MegaLinks in Criminal Justice

Deja una respuesta

Tu dirección de correo electrónico no será publicada. Los campos obligatorios están marcados con *