Algunas críticas y defensas al sistema de libre valoración de la prueba

Fingers are not the only things that leave prints. Tools, shoes, tires, teeth, and other things can leave prints, marks, and impressions in or on various substances, and these marks can provide clues to the knowledgeable character.

Tools can usually be identified by comparing them to the impression and looking for distinc- tive nicks, marks, scoring, or other distinguishing features (though most often these features are microscopic; at the microscopic level, every tool is distinct). However, an investigator should never “fit” the tool into the impression in an attempt to match them, since this may alter the mark and ruin the evidence. Depending on the nature of the toolmark, an expert may also be able to determine what sort of tool made the mark.

Other impressions or tracks can be made by things like shoes, cloth, and tires. When they appre- hend a suspect, investigators can compare the print

in question with the object that might have made it (for example, they can compare a footprint to the suspect’s shoes). If a good enough print is obtained, it may also be possible to compare it to a data- base of known prints and identify it by type (for example, as a Brand X tire rather than a Brand Y tire). Footprints may also tell a trained investigator whether the subject was walking or running, how tall he is, and similar facts.

In appropriate instances, Tracking may serve as a Complementary Skill when a character attempts to determine who or what created a print or track on the ground. SS: Print And Impression Identification is also a Complementary Skill.

SOIL (FORENSIC GEOLOGY)

Forensic scientists try to identify soil as coming from a particular location, thereby link- ing soil samples found at a crime scene to soil found in another location. The more unique a soil sample is, the easier it is to identify it as coming from a particular place. Criminalists examine soil characteristics such as color, min- eral content, the size of the soil grains, soil den- sity, and soil components (foreign matter). They can also examine objects manufactured from minerals or soil, such as bricks, plaster, concrete, and some types of insulation. The most common test for comparing soil samples is the density- gradient tube technique, but other tests are avail- able and they are all best used in combination.

Unfortunately, relatively little data is available to indicate how likely it would be to find two basi- cally indistinguishable soil samples from different areas. Some studies indicate that, at least in some areas, soil samples are relatively unique (thus allow- ing the criminalist to easily identify the area where a sample comes from). Characters who need to make extensive use of soil evidence may want to invest some points in studying a particularly area to determine soil variability (bought as KS: [Area] Soil Variability, for use as a Complementary Skill).

SS: Geology is a Complementary Skill when analyzing soil. City Knowledge or Area Knowledge may also help identify the origin of soil samples.

TAPE

Criminals frequently use tape, particularly duct tape, in crimes — to bind victims, to blind- fold them, to hold the parts of a bomb together. By comparing tape found at a crime scene to known samples, and by comparing torn or cut tape ends to see if they fit together, the criminalist can uncover valuable clues. Tape is also a good source of finger- prints and fiber evidence.

Other Rules

EQUIPMENT

While some uses of Criminology (such as gathering evidence, analyzing suspects’ motives and behavior, and so on) don’t require any equip- ment (or at best minimal equipment), analyzing evidence is different. To properly analyze most

forms of evidence a character needs a crime labora- tory equipped with microscopes, chemistry sup- plies, fingerprinting materials, and other tools, plus access to reference materials.

Contents Of A Crime Laboratory

Here’s a brief description of some of the equip- ment a character might have in his criminalistics laboratory. If a character cannot obtain some of the equipment described below, the GM can impose a negative modifier on Criminology rolls made when using the lab, or can simply rule that the character cannot perform some of the tests described above. Chromatograph: A chromatograph separates and identifies chemical compounds. The substance to be identified is placed in a stationary medium. A moving medium passes over or through the stationary medium, and separates the various sub- stances in the sample. The chromatograph cannot by itself identify the tested sample, but when linked with a mass spectrometer it can provide unques- tionable identifications of thousands of substances.

Criminalists use both gas and thin-layer chro- matographs — the former to identify gases and vaporized materials, the latter to identify liquid mixtures or dissolved solids. A third type, high-per- formance liquid chromatography, can be performed at room temperature (the samples do not have to be vaporized or heated), and so is used when charac- ters must analyze explosives and other heat-sensi- tive substances.

Microscopes: No crime laboratory would be complete without several different types of micro-

scopes. Besides the standard compound micro-

scope, criminalists also use the comparison micro- scope (which allows a side-by-side comparison of two objects for identifying marks), the stereoscopic microscope (a low-powered microscope which provides a three-dimensional image of the viewed object, good for viewing bulky items), and the scan- ning electron microscope (which uses electrons to display images of very tiny objects). Microspectro- photometers combine a microscope and a spectro- photometer.

Neutron Activation Analysis: Another tech- nique for identifying substances is neutron activa-

tion analysis. This process involves bombarding a

sample with neutrons so a scientist can measure the resultant gamma ray radioactivity and identify the sample. Unlike chromatography, this process doesn’t destroy the sample.

Neutron activation analysis works on minute quantities of a substance. Modern equipment is so sensitive it can identify substances from even the tiniest traces. Some types can identify a substance from only a 100-nanogram sample.

Spectrophotometer: A spectrophotometer measures the “absorption spectrum” of a substance — the quantity of light it absorbs. Each substance’s absorption spectrum is distinctive and identifiable. Once a readout is obtained, it is compared to a vast library of known readouts to identify the tested substance. Similarly, characters can use emission spectrographs and atomoic absorption spectropho- tometers to analyze the light selectively absorbed and emitted by the various elements. Spectropho-

tometers can work with ultraviolet, visible, or infra- red light. Miniaturized versions (weighing about 70 pounds) can even be used in the field.

Lie Detectors

While devices designed to detect whether someone’s telling the truth aren’t exactly criminal- istic tools, characters might use them to investigate and solve crimes.

The polygraph, or lie detector, has been avail- able since the 1920s. It works by measuring emo- tional responses such as breath rate, heart rate, sweatiness, and blood pressure that tend to indicate the subject is being deceptive. Unfortunately, that means a nervous person who’s telling the truth may register false positives, while a cool-as-a-cucumber liar could appear honest. Thus, while polygraphs may prove helpful in some cases, their results are not reliable enough to be admitted as evidence in most courts in most situations.

Scientists have developed a technique they think will prove more accurate: “brain fingerprint- ing.” This devices “reads” the subject’s mind, regis- tering signals that the brain emits when it perceives things it’s familiar with. If a subject’s mind doesn’t indicate familiarity with the circumstances, envi- ronment, and objects related to a crime, it’s prob- able he didn’t commit that crime. The results of the device have been admitted in some courts.