The Forensic Scientist’s report for use in court

1. The Forensic Scientist’s report for use in court Help with P8 M8 D8

2. Types of evidence • Real evidence: often referred to as physical evidence, consists of items known in court as “exhibits”, such as knife used in a murder. • Documentary evidence: statements from witnesses, video recordings • Witness evidence: May be presented orally in court (e.g. Expert witness)

3. Expert witness • Evidence contains both fact and, in areas that are outside the common knowledge of the court, their personal opinion • Written reports must be written in such a way that is understandable to non-scientists, such as solicitors, the police and the jury or magistrates hearing the case

4. Help with P8 • Must download witness statement pro-forma from moodle (under resources for P8 M8 D8) • Need to make sure witness statement is filled with details listed on next two slides

5. Expert witness report should contain the following: • Full name, work address and qualifications of the forensic scientist responsible for compiling the report • Statement of truth verifying the report- signed and dated • Enough background details to the case to place tests techniques carried out in context • Catalogue of items of evidence received for forensic examination • An explanation of any relevant technical issues

6. Expert witness report should contain the following: • A brief description of the experiments conducted, the reason why they were carried out and a summary of results performed • An interpretation of the results of the forensic tests conducted (May involve personal opinions) • If more than one conclusion is feasible then recommendation on which one is most probable • A summary of conclusions reached

7. Case scenario (to use for witness statement) • The police of a small village in Worcestershire are concerned that a number of crimes have been reported within hours and the police are suspicious of this. These crimes include, the local river water being contaminated with an unknown chemical, an apparent suicide of a young woman in woods that are located behind the victim’s home and blood found in the woods. • Further-more, the woman worked for a local paint manufacturing company and she had confessed to her friends that this company were disposing of harmful paint onto the river

8. Practicals carried out • P3: Analysing river water using chromatography (to identify if river water was contaminated with dangerous or safe purple paint) • P7: Analysing blood samples: To determine if blood stains found in wood were the same of different blood type to four suspect patients in a local hospital • P5: Analysing handwriting: To determine if suicide note was genuine or fraud

9. Task: summarise your findings

10. Help with M8 • Justify your conclusions for practicals carried out for P3, P5 and P7 • Need to address the questions listed on the next two slides

11. M8: Justify your conclusions • What was your conclusion to the chromatography experiment from P3? e.g. The river water has been contaminated with the toxic paint called Purple Haze. • Why did you reach this conclusion? (refer to results) e.g. The chromatogram shows that there are two components that both river water and purple haze have, these two components have the Rf values 0.8 and 0.5 • What was your conclusion to the colorimetry experiment from P3? • Why did you reach this conclusion? (refer to results)

12. M8: Justify your conclusions • What was your conclusion to the handwriting analysis experiment from P5? • Why did you reach this conclusion? (refer to results) • What was your conclusion to the blood typing experiment from P7? • Why did you reach this conclusion? (refer to results)

13. Help with D8: • Evaluate your findings for chromatography (P3), colorimetry (P3), blood typing (P7) and hand writing analysis (P5) • To do this you need to identify where errors could have occurred AND what type of errors could have occurred. • Then consider how much these errors may have affected your results/findings and how these errors may have affected your results/findings.

14. Random errors Random errors in experimental measurements are caused by unknown and unpredictable changes in the experiment. These changes may occur in the measuring instruments or in the environmental conditions How should we deal with this? Take more data. Random errors can be evaluated through statistical analysis and can be reduced by averaging over a large number of observations.

15. Systematic errors Systematic errors in experimental observations usually come from the measuring instruments. They may occur because: there is something wrong with the instrument or its data handling system, or because the instrument is wrongly used by the experimenter How should we deal with this? Systematic errors are difficult to detect and cannot be analysed statistically, because all of the data is off in the same direction (either too high or too low). Spotting and correcting for systematic error takes a lot of care.

16. Gross error Gross errors are undetected mistakes that cause a measurement to be very much farther from the mean measurement than other measurements. For example, if you were supposed to get the mass of a baseball and you chose a softball from the table to mass, that's a gross error that will skew your results.

17. Accuracy • Accuracy of a measurement system is how close its measurements are to the true value. • Eliminating the systematic errors improves accuracy but does not change precision. • You can still achieve accuracy with random errors

18. Precision • The precisionof a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results. • if an experiment contains a systematic error, then increasing the number of measurements made should increase precision but does not improve accuracy

19. What makes a measurement valid? • A measurement system can be accurate but not precise, precise but not accurate, neither, or both • A measurement system is designated valid if it is both accurate and precise