Medicolegal Trace Evidence

Trace evidence is an important category of crime scene evidence in the sense that it is the most direct evidence related to the suspected criminal act. Owing to the great improvements made in medical science and technology over the past few decades, trace evidence or forensic evidence, as it is commonly referred to in legal parlance has assumed an increasing degree of importance and has often proved to be the deciding factor that leads to either a conviction or an acquittal.

In its most basic sense trace evidence entails all kinds of physical evidence found in the crime scene (anything that leaves a trace) as for example blood-stained clothes, hair samples, semen etc. etc. Often, trace evidence is very minute and delicate in nature and only trained forensic experts and detectives can obtain them from the scene of crime. For certain kinds of evidence like semen stains for example, it is as important to preserve the recovered evidence as it is to get them in the first place  because over time the sample may become impossible to analyse clearly owing to degeneration and contamination and hence crucial evidence may be lost. So, while the significance of trace evidence cannot be understated, it is also a fact that most modern jurisdictions spend vast sums of money in acquiring the proper technology, medical and forensic personnel, setting up laboratories and crime research divisions  so that information gained from this evidence is not wasted. Most courts across various jurisdictions around the world require trace evidence to be authentic and capable of independent corroboration because otherwise they are liable to be rejected as evidence. Thus whoever wishes to rely on information gleaned from trace evidence found on the scene of crime, has to meet the various standards set by courts regarding its admissibility. Hence unsurprisingly, crime research laboratories are now equipped with state of the art technology to conduct the most appropriate and accurate tests on samples retrieved from the crime scene, so that when they are presented as evidence in a court of law, they are not rejected on grounds of spuriousness or inconclusiveness. Some of the more popular and universally accepted tests are as follows Stereoscopic Microscopy, Polarized Light Microscopy (PLM), Ultraviolet Light Microscopy, Scanning Electron Microscopy (SEMEDX), Fourier Transform Infrared Spectroscopy (FT-IR), Gas Chromatography  Mass Spectrometry (GCMS), Pyrolysis Gas Chromatography (PGC), Ion Chromatography (IC), and Microspectrophotometry. Certain kinds of trace evidence like questioned documents (i.e. samples necessary for handwriting analysis) are such an universal feature of most crime scenes that local police departments often have research divisions devoted entirely to that. Also in cases of trace evidence that seek to directly implicate the involvement of the accused in the crime, like fingerprints and blood stains etc. etc. it is of particular importance that the samples so obtained are compared with corresponding samples taken from the accuseds body at the earliest, so that a measure of corroboration may be achieved. In a nutshell, information gathered on close examination of trace evidence may help the investigation in any or all of the following ways
It establishes the areaterritorial extent of the crime scene.

It determines the physical attributes of the perpetrator(s).
It provides hints as to what weapon was used for the commission of the crime (in case of violent bodily crimes).

Supporting or endorsing witness statements i.e. checking them for consistency.

It helps to establish common links if there are more than one crime scene areas (for e.g. blood stains found at the scene of murder and those obtained at the place where the victims body was disposed off.)

Following Edmund Locards principle, which states that when there is contact between two or more items there is a always an exchange of the respective characteristics of each item, it can be said that whenever there is a crime, the criminal always leaves a trace or pattern behind, which is unique to him. Consequently, if investigators are able to discover these traces then there is a good chance that it will lead them in the direction of the offender. Of course, as has been mentioned before, a person must be tried by a competent court before he can be declared guilty of an offence  and for this the prosecution must prove inter alia that the trace evidence on hand conclusively determines the guilt of the accused.

Even if some trace evidence is admitted in a court of law, it does not ensure that it is a smooth run for the prosecution thereafter. Such evidence must be backed up by corroborative witness testimony and more importantly, it must stand the test of cross-examination by any expert appearing for the opposite side. If the defense is able to introduce even a small hint of ambiguity in the findings presented as evidence, then the prosecution will have a difficult time convincing a judge and jury of its veracity. However, on the other hand, if the prosecution can establish the authenticity of the trace sample and put forth any information that adversely connects the accused with that sample (as for e.g. a DNA match) then the chances of conviction of the latter increases correspondingly. In fact cases have sometimes been decided on the basis of strong, irrefutable and unimpeachable trace evidence submitted by the prosecution (which must be verified by an independent expert to the satisfaction of the court). For example, in State v. Todd, 6 P.3d 86 (Wash. Ct. App. Div. 3 2000), where the prosecution was able to show that circumstances were such that the accused had access to a moving object and that such an object had been used in the commission of the crime and subsequently the accuseds fingerprints were found on it  the Court ruled that the fingerprint analysis submitted as evidence was enough to convict the accused. Also, in another case involving the presentation of finger print evidence (People v. Hirsch, 280 A.D.2d 612, 720 N.Y.S.2d ), the court held that fingerprint evidence, although circumstantial in nature, is sufficient proof if it leads to a conclusion of guilt beyond a reasonable doubt and excludes every reasonable hypothesis of innocence.Analogously, in a case (People v. Sutherland, 223 Ill. 2d 187, 307 Ill. Dec. 524, 860 N.E.2d 178 (2006)) where an accused was tried, inter alia, for murder and aggravated sexual assault, and the accuseds pubic hair structure matched that of strands found on the victims body, the Court ruled that such evidence was enough to reasonably infer that the accused had committed such an assault (taking into consideration other evidence).

As is apparent from the above case-laws, when trace evidence proves conclusive it is a very compelling piece of evidence indeed. However, conviction depends on whether the Court-appointed independent expert corroborates the analysis of the State laboratories and where the expert has failed to reach a decisive conclusion and the prosecution has failed to clarify the latters doubts as to its veracity  then such evidence falls flat.

Another issue that is frequently raised when trace evidence is adduced in a trial, is whether the constitutional right of the accused to be protected from self-incrimination, under the Fourth and Fifth Amendments to the Constituion of the United States, had been safeguarded during the conduct of the entire investigation. Particularly in cases where a suspect is asked to give fingerprint samples, blood samples etc. etc. this question has arisen time and again in various courts. In Jones v. State, 277 Ga. 36, 586 S.E.2d 224 (2003) for instance, it was held by the Court that handwipings that revealed presence of gunshot residue were not an unconstitutional search or seizure, and expert testimony concerning results of tests did not violate constitutional privilege against self-incrimination. Evidence obtained improperly in this regard (i.e. without following due process norms) may be struck down by the Court. But it is generally sustained where a warrant has been obtained or, (as was held in State v. Campbell, (1968) 281 Minn 1, 161 NW2d 47) the accused himself had waived his Fifth Amendment right by consenting to samples being taken from his body, in which case he cannot claim violation of his constitutional rights at a subsequent stage. However, in a pioneering case, Schmerber v. California, 384 U.S. 757 (1966) 384 U.S. 757 (1966), by a majority opinion delivered by Justice William J. Brennan, Jr., the US Supreme Court held that the doctrine of self-incrimination applied only to compelled communications and testimony and that a blood test did not fall under any of the above categories. Also, as far as search and seizure operations under the Fourth Amendment provisions of the US Constitution are concerned it is now settled law that items recovered from a crime scene under a search warrant does not violate the accuseds rights under the Constitution and that such items can be used as evidence against the latter.

However, as is evident from the more recent case-laws mentioned above, the judicial weight of the opinion delivered in Schmerber has diluted greatly and Courts are now apprehensive of convicting a person based on evidence in the form of a blood sample alone, especially one that has been obtained without a warrant or informed consent.

Trace evidence has thus assumed an increasing amount of significance ever since courts have started recognizing the scientific minutae that accompanies any trace analysis, be it a ballistics report or a blood test analysis. Owing to the strict standards imposed by most courts, it must be handled by professional and literally treated with kid gloves so as not to tarnish the evidentiary value of the sample. In fact these kid gloves come in a variety of tools  like brushes, forceps, gloves, chemicals that reveal traces of blood etc. etc.  all of which enables the seasoned crime scene investigator to deduce various elements of the crime and recreate the entire chain of events.

Irrespective of whether it is in the form of hairs and fibers, glass, paints, firearms and explosives, blood and other bodily fluids, bitemarks, arson debris, footprints etc. etc.  crime scene investigators have to take the utmost care to obtain and preserve it in materially the same form as it was found in the crime scene.


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