The “forensic” in “forensic science” – part A

The approach taken in activity two leads us to the conclusion that forensic science is indeed a legitimate scientific activity. Because the processes that are intrinsic to it mirror those of the scientific method. But what is it that distinguishes it as an identifiable discipline within the sciences? The answer is not so much what but why. In week one, we dealt with the definition of crime scene examination by focusing on its purpose, namely reconstruction of the events that created the crime scene. And we can take the same approach with forensic science as a whole. Crime scene reconstruction can be viewed as one example of the overall purpose of forensic science.

Which is, “To provide objective information on which reliable evidence based decisions can be made.” This definition is consistent with the criminal incident approach that we have adopted throughout. And does not encompass areas such as criminal intelligence. The many civil law or regulatory applications of scientific investigations have also not been covered. In week one, we discussed what was meant by real evidence in contrast to testimonial evidence. And showed that forensic science is an important source of real evidence. Forensic science evidence itself can be classified as being one of three types– inceptive, exclusionary, corroborative. Inceptive evidence– literally meaning, “from the beginning,” is evidence that shows that an offence has been committed.

It is easily illustrated with reference to, for example, arson and drugs. We didn’t cover arson in this introduction to forensic science. But it is the crime of deliberately setting fire to property. The starting point of the forensic science investigation is therefore to challenge the hypothesis that the fire was initiated by accidental or natural causes. Sometimes nature and accident come together dramatically as in the Ash Wednesday bushfires in Australia in February 1983 which were responsible for 75 fatalities. The source of many of the outbreaks was traced to high winds and temperatures resulting in the sagging and subsequent clashing of power lines causing sparks that ignited the tinder, dry, surrounding vegetation.

Because arson involves the deliberate initiation of the fire, the mechanism of that initiation is the focus of the forensic investigation. Finding traces of accelerant associated with one or more areas of initiation of a building fire is an example of inceptive evidence that the event was most likely arson. Whereas finding a faulty electrical switch at a single area of initiation is more likely to be evidence of accidental rather than deliberate causes. We did cover drugs. And the possession of an illicit drug or prohibited precursor is in itself an offence. The inceptive evidence here results from the chemical– or in some cases botanical– identification of the prohibited substance.

In week three, we saw how forensic biology can contribute to the unravelling of events in cases of crimes against the person. There were main areas covered. Blood pattern analysis, where the physical nature of blood stains can sometimes provide information on how the stain was created. And DNA profiling, which can provide very compelling information on the identity of the person from whom the biological material originated. The scientific method can be applied to the evaluation of all of these as we formulate and test hypotheses to explain our findings. A man calls the police to report that his wife has fallen to the ground when cleaning the window of the bathroom of their 4th floor apartment.

But luminol testing of the apparently clean bathroom shows blood smears on the inner window ledge. The husband had struck his wife on the head and pushed her out. There are clear cut situations where the forensic science evidence eliminates an event or a person. However, most of the time forensic evidence is neither inceptive nor is it exclusionary. The inceptive evidence is usually a report from a victim or witness. And evidence arising from a subsequent forensic science investigation which will either be exclusionary or be in keeping with what may have been expected. What we have to do now is to consider how to deal with this non-exclusionary or corroborative evidence. There are many limitations to corroborative evidence.

And we shall explore this shortly. But first of all, we need to discuss at different classification of evidence, namely associative evidence.

Associative evidence is exactly what the name implies. It is about evidence that can link people with people, people with objects, or people with places. This is the basis of Kirk’s concept of making the things at the crime scene talk, his silent witnesses. But is this really any more reliable than evidence from eyewitnesses? As we have seen previously, yes. Because the evidence is or should be objective and verifiable. But that is not the same as saying that it is always absolutely correct. There are two problems. The first being like all inferences drawn from hypotheses, the conclusions drawn from the things are only as good as the state of knowledge at the time.

The second is that those who use the evidence would like to know what weight to place on it. And that often comes down to the question of how commonplace is the thing. And what is the probability that it was encountered by chance. Assessing the weight that can be ascribed to corroborative evidence by means of statistical testing is a complex area. And one that is not entirely free from controversy. It would require another six week MOOC class to deal with adequately, and will not be considered here. Instead, we will look at four pieces of evidence from the Murder by the Loch case in the order. The footwear mark by the jetty. The tyre tracks by the jetty.

The physical location of the points of origin of the blood spatters in the car. The chemicals found at the cottage. Amongst the potential evidence recovered from examination at the scene by the jetty was a partial footwear mark. The mark consisted of an impression in the soft ground. But was too shallow to cast. It was recorded by photography. And the mark compared with the shoes worn by Mr. Ward. The comparisons do not exclude the mark being made by the shoe. However, they are dress shoes with plain soles and are quite new with no distinguishing marks from damage or repairs. The shoes were clean when taken by the investigators. They are a common brand purchased from a large retail chain.

Since we cannot exclude the shoes from having made the mark in the soft ground, this becomes corroborative evidence for Mr. Ward. Not only being at the jetty, but being outside the car. On the other hand, there is nothing very specific about the association. There is not enough information in the photographs to say that these shoes did not make the impression. But is there enough to make the conclusion that they did so, a reasonable one? There was another footwear impression found by the jetty. This one was from a sports shoe with a very distinctive sole pattern. And could not have been made by Mr. Ward’s footwear, or that worn by any of the scene investigators.

The collection of tyre mark impressions in the soft ground by the jetty, and the creation of reference marks at the crime scene garage have already been discussed. In contrast to the footwear impression that may have been made by Mr. Ward, these marks are very clear. There can be no reasonable doubt that they were made by the same make and size of tyre as those fitted to Mr. Ward’s car. Furthermore, his car is of a make and model that had only recently been introduced to the UK market.

Our degree of comfort with the corroborative evidence will have risen as we have moved from an indistinct footwear mark that may have been made by a shoe widely available to very distinctive marks from a fairly rare model of motor vehicle. But we’re still somewhat short of being able to say, yes. These marks came from one of the tyres on Mr. Ward’s car. For that, we would need some specific, distinguishing mark such as a damage or a stone trapped in the tread. Tiny spots of blood were found on various surfaces in the front of the car. We saw in week three that pinpoint spots of blood are typical of those produced by a high impact injury such as a gunshot.

We saw in the case narrative that the spatters found in the car had two points of origin. With blood with the same DNA profile as Mr. Ward originating from the left shoulder region of the driver’s seat. And blood with the same DNA profile as Mrs. Ward’s originating from an area between the seat and at approximately the level of the dashboard. The conclusion is inescapable that the stains were created by the impact of the bullet that killed Mrs. Ward. Being fired from inside the car, and not from someone outside by the passenger door. We have the most compelling corroborative evidence because of the physical nature of the stains together with the DNA profile. But corroboration of what?

It is certainly corroborative of Mrs. Ward being shot inside the car. And exclusionary of Mr. Ward’s account of events. But does it tell us anything about whether he pulled the trigger? Identification of illicit drugs and chemicals used in their manufacture was one of the examples given as illustrating inceptive evidence. It is included here because it provides a nice counterpoint to the uncertainties in our corroborative evidence examples. And to illustrate that the evidence categorizations are somewhat arbitrary. The same things can provide evidence of different types. In this case, there was a suspicion that Dougan and was involved in some way in the manufacture and distribution of illicit drugs.

And that finding him present at what the chemistry shows is indeed a drugs lab is the strongest of all of the four illustrations of corroborative evidence.