Consider the latent fingerprint. Obviously, identifying its source, or more often in review work, verifying the original examiner's work, is important. But a latent may tell much more. With a properly documented latent fingerprint, it may be analyzed to determine the action that led to its deposition...was it the result of a hand facing in or out of a window, for example. Was it one act, or a hesitating act, or involve slippage, or some other factor. Perhaps such information may have no value to a case, but other times, it way be very important to determining the role of the party responsible for it. At the entry to a burglary, a latent which can be determined to have been made from the inside of the point of entry, especially if it is pointing out, when the originator has legitimate access to the location, may argue against guilt. In one of the most egregious incidents of an investigator planting evidence, the examiner noted that the latent was too clean, unnaturally perfect - and as a result found that the "latent" had actually been manufactured by an investigator from a fingerprint card to frame the "suspect."
In firearms cases, the evidence bullet is often too badly damaged to effect an identification with a firearm. However, it may still have sufficient detail to permit elimination. Or, it may have sufficient detail top permit its use as a reference to general rifling characteristic files; here, the class characteristics of a huge variety of models of firearms are stored. By careful measurement the examiner can establish number of lands and grooves, direction of twist, and width of lands and grooves. This information may then be researched against a general rifling characteristic file, and a list of firearms that may be the same model generated. This is especially valuable if a suspect firearm is known, as the lack of appearance on the list may well speak to elimination, even though the presence of the firearm on the list does not speak to identification, as it will just be one of thousands that share these same class characteristics.
Careful technical review may well have mitigating value. For example, possession of one blasting cap or an entire case of high explosives is the same under the law. However, an explanation of the difference in destructiveness of them will educate the court to the wide dissimilarities of the two.
A review of the actual crime scene may reflect otherwise missed aspects of an incident. In a shooting, is the damage consistent with the firearm and trajectory? The criminalist may attempt to reconstruct or even recreate the scene, to determine if the results using the same elements as were purportedly used in an incident can be replicated.
For counsel, to learn that the evidence argues against the story upon which the theory of the case is powerful evidence of, if not lack of guilt, that at least there are serious questions as to the basis of the accusation. Conversely, if the criminalist's work does sustain the existing case, it provides counsel with the knowledge that the opposing case is built on a strong foundation, and permit counsel to pursue a different strategy.
It is neither counsel nor an investigator's role to know what to ask for. Instead, they should make a more open ended request of their forensic specialist. If the question is to verify the work of previous criminalistic analysis, then that is what the consultant is being contracted to deliver. Rather, ask the consultant to review for the purpose of verification previous analyses, but also ask the consultant to review the evidence itself, and to determine what other information it may reveal of value. It will add some time to the work of the criminalist, and perhaps some other expense...but it may also provide important information for inclusion in the case preparation.
