Forensic laboratory results

Limitations on the Interpretation of Forensic Laboratory Results (Mr. C. R. Mldklff)... 

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Such results have been used to both convict and acquit suspects and, in other cases, to establish paternity with an extraordinary degree of certainty. The impact of these procedures on court cases will continue to grow as societies agree on the standards and as formal methods become widely established in forensic laboratories. Even decades-old murder mysteries... 

The course on crime scene investigation will be offered by the College of Criminal Justice and will emphasize the importance of scene examination and evidence sampling. An improper sampling method can invalidate the results of the forensic laboratory. 

At the February meeting of the American Academy of Forensic Sciences in Dallas, Texas, the Criminalistics Section supported a resolution that the Forensic Sciences Foundation develop a concept paper for a national system of crime laboratory proficiency testing This, subsequently, resulted in a grant award to the Foundation for an eighteen-month study which will test the feasibility of regular proficiency testing in the nation s forensic laboratories. 

Forensic laboratories use the system of chain of custody to demonstrate in court that the samples have, at all times, been held securely by authorised persons and that no tampering with the evidence has taken place in the laboratory. In addition, it is essential that one can demonstrate that the results of the analysis relate to the correct sample and that it can be traced back to the suspect or the site from which it originated. 

In most forensic laboratories, the largest amount of HPLC time is taken up with the analyses of drugs of abuse (often called street drugs) i.e. amphetamines, heroin, cocaine, LSD, etc. The purpose of any drug s HPLC analysis is to confirm the identity of drug and provide a quantitative result. With the exception of LSD, relatively large quantities of a drug sample are usually available and UV detection is preferred since it offers... 

The analyst can improve the identification of solutes or discrimination between samples by studying the multi-wavelength plots or spectra of the eluted components. Transformation of spectral data to yield derivative spectra have been used to improve sample discrimination, whilst a plot of the ratio of absorbances for two selected wavelengths is an excellent method for confirming the homogeneity of chromatographic peaks. However, there is a trend in forensic laboratories to use and develop techniques whereby the spectral data are reduced to a smaller number of numerical values. Results in this format at easier to compare and present in court and furthermore can be evaluated statistically. 

In the analysis of air for pollutants, for example, some of the compounds may be present in too low concentrations to be analysed straightaway. In such a case, it becomes necessary to raise concentrations of those compounds to the level where the required analysis becomes practical. Situation of a different type may arise in certain other analyses. Thus in the analysis of river water for metals that are present in trace concentrations, erroneous results are obtained because of the interference caused in the analysis by organic compounds contained in the sample. In a situation like this interfering substances have to be removed before the analysis can be performed. Also, many analyses now carried out daily in the clinical and forensic laboratories all over the world involve separation as an integral part of the procedure. 

Mr. Mldklff introduces this topic In the following manner Recently, increasing concerns have been addressed about the reliability of results from forensic laboratories. One question of particular concern which may be asked is the extent to which these poor results are attributable to attempts to push detection limits beyond the limits of reasonable scientific certainty, making interpretation of results tenuous. 

By contrast. In Che forensic laboratory, Che quantity of sample Is often limited and additional material Is unobtainable. As a result, there Is little opportunity for analytical methodology modification and matrix adjustment or optimization. Further, Che matrix Itself Is variable as In cases Involving arson. 

Can you imagine going to court with results that you are not completely sure about in terms of validity and reliability Imagine the situation where you have been asked to attend the coroner s court in relation to a suspected drug overdose You are in the witness box and you are asked to confirm that your results indicate that John Doe may have died from an overdose of heroin. His family is in court and your answer is, I think so, but I can t really be sure it was heroin and I can t be sure about the amount exactly . Clearly, this answer is not acceptable and it would not take many appearances at court of this type for you to lose any credibility as an expert witness and to bring your laboratory into disrepute. In order to avoid these types of situations, it is normal for forensic laboratories to implement a set of principles that ensure that results are valid, reliable, and repeatable. This forms part of the company s overarching quality system (see Chapter 9). One of the ways in which a laboratory can ensure that measurement is valid and fit for purpose is to adopt the valid analytical measurement (VAM) system. 

The overview provided in this chapter highlights the fundamental principles of the IRMS technique and the significant value that it can play in complex forensic investigations. This chapter also addresses some of the key considerations for the installation and implementation of the technique into an operational forensic laboratory. The current status of the technique for a number of the forensic applications discussed in this chapter allow for the use of IRMS results for intelligence purposes however for others, continued research is required to ensure the generation of court reportable results and also to continue the path toward broader forensic casework application. 

Atomic absorption remains a staple of forensic chemistry, given its low cost, simple operation, and easy maintenance. The limitations are related to versatility. Unless multielement lamps are used, only one element can be tested for at a time, and each element requires a separate lamp and instrument optimization. For small target lists such as a list of barium, antimony, and lead for GSR, this is not onerous, but still is inconvenient. Limits of detection are in the low-ppm to high-ppb range for most elements, As a result, a few forensic laboratories have turned to inductively coupled plasma atomic emission spectroscopy (ICP-AES) for additional elemental analysis capability. 

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