Forensic Chemical Analysis FSC 444 Introduc7on to Forensic Analysis and Analysis of Color
Text reading: Chapter 1, also xv-‐xviii Quote from textbook (page xv): “If this is your first course in chemistry, get out while you s5ll can!” True, you should have taken General Chemistry – that’s a prerequisite. The book preface also says that you should have taken organic chemistry, but we will not be covering the sec7ons that require this. So you need not have taken organic.
About this course: This is an analy7cal chemistry class with focus on techniques used in forensic science. Q: If you have a B.S. in Chemistry, you presumably took analy7cal chemistry, so why do we require you to take this course? A: Forensic science is all about analysis, so some repe77on in analy7cal chemistry is a good thing. And unless you took a forensic chemical analysis class, at least some of the methods in this class will likely be new. We will also do several case studies.
Laboratory Most of the material in the online por7on of this course will be “lecture” material that serves to support the experiments done in the laboratory. The associated reading in the textbook is listed in the syllabus. To some extent, more direct notes about the laboratory will also be included here. These will aim to clarify procedures to be done in lab, explain the purpose for steps, and go through associated calcula7ons.
Laboratory Reports The lab reports in this course will likely differ from what you are used to in chemistry classes. The narra7ve por7on of the reports for this class should be concise, containing only the results – without all the details of how the results were obtained. Why? When a forensic scien7st submits a report to be used in court, the report needs to be concise and understandable by non-‐scien7sts. Reports in this class, in general, should be prepared with the same goal.
Laboratory Reports Courtroom lab reports do s7ll need to include the details, but these are oVen provided as appendices. Likewise, our reports will contain all notes wriWen during the lab, appearing aVer the narra7ve. These notes will be wriWen on loose sheets of note paper that will be available in the lab. Finally, the reports will also include answers to prelab and postlab ques7ons. In general, all prelab and postlab ques7ons in the lab manual should be answered, though occasional subs7tu7ons will be made.
Laboratory Reports So – you will not need a notebook for this course. You may find use from 7me to 7me for a digital camera. The one in your cell phone may be fine, and if you don’t have one, you can borrow mine or one from another student. In several experiments (those involving instruments), it will also be convenient for you to have a USB flash drive to save your data files. In week 2, you can also take your color percep7on test results with you.
Introduc)on to Forensic Analysis (Bell Ch. 1) Q: What is the origin of the word “forensic”? A: Click here to find out. “Forensic” comes from “forum” and meant roughly “public presenta7on”. The Roman forum was a precursor to our court system, and today “forensic” as an adjec7ve means the legal aspects of the word that follows. “Forensic science” is science – oVen analy7cal chemistry – applied to the law.
Q: What is the goal of a forensic chemist’s tests? A: That depends on the evidence. But the goals are typically both qualita)ve and quan)ta)ve. Qualita7ve: Does this white powder contain cocaine? What else does it contain? Quan7ta7ve: How much cocaine is in the sample? Ques7ons can also be compara7ve: Does this cocaine match that taken in last week’s bust?
Q: Cocaine is an organic compound. How can one hope to compare different samples – shouldn’t they all be the same? A: No, cocaine can be pure but is usually mixed with cuang agents: ⦶ diluents (starch, baking soda, etc.) ⦶ adulterants (other drugs, like caffeine) ⦶ impuri7es (from source or processing) So a given batch of cocaine has a “fingerprint” defined by the percentages of all components!
I asked a forensic chemist at the Onondaga County crime lab how oVen they analyze for the other components, and he said almost never. They usually need only measure the amount of the illegal substance.
Forensic science uses many comparison tests: • Ballis7cs (done on a comparison microscope) • Hair, fibers • Glass • Handwri7ng analysis • DNA • Etc. The usual point of forensic comparisons is to be able to say whether two samples, typically one from a crime scene and the other from a suspect or vic7m, have the same source. Q: What are the possible answers to the same source ques7on? A: Yes, no, or maybe.
Q: Maybe?? Does a forensic scien7st on the stand ever say “maybe”? A: Well, “maybe” is not the best word to use in court. BeWer: “is consistent with” Even beWer, if possible: “is consistent with, and 95% of the popula7on is excluded” “Excluded” is the same as “no”. “The suspect is excluded as the source of ______.” “Yes” is rarely possible. “Consistent” with a high probability is usually the best one can do.
Goals of forensic analysis: • Iden7fica7on (cocaine, wool, dog hair) • Classifica7on (Shetland wool, poodle dog hair) • Individualiza7on (hair from this dog)
By defini7on, forensic science involves the interac7on between Science and The Law. This interac7on is not always smooth and has built-‐in tensions. Science, by its nature, involves uncertainty, while the law seeks certainty (beyond a reasonable doubt for a criminal case). Scien7st strive to understand a situa7on, while the law must reach a decision – even if understanding is not aWainable. So rules of the court impact the way forensic scien7sts must work.
Rules of the court: • Admissibility – only accepted (Frye) or compelling (Daubert) methods are admissible. • Chain of custody – the scien7fic results are meaningless if there is any real or perceived chance of tampering. (This is why the Onondaga County Center for Forensic Sciences does not provide tours!)
• Cer7fica7on – of scien7sts and of methods. • Preserva7on of evidence – for second opinion or appeal. A small sample cannot be used up in the analysis.
Q: Which type of evidence is beWer, circumstan7al or direct? A: Most will say direct, but it really depends! Direct evidence usually means that an eyewitness can say the suspect was at the scene. But eyewitnesses are known to make mistakes, even if they say they are sure. Project Innocence data suggests this is the most common reason for wrongful convic7ons. All forensic evidence is circumstan7al – an inference must be made concerning the meaning rela7ve to innocence or guilt. But the result and the inference can be very strong! (For example, DNA of suspect found under vic7ms fingernails!)
Forensic Mindset To be effec7ve, a forensic scien7st must have an appropriate mindset: • Assume nothing • Use all available tools (as needed; this includes unfamiliar tools in other fields) • Be crea7ve (as needed) • Consult others • Be persistent
The “as needed” is very important. A case that uses standard and cer7fied methods is much stronger, unless these methods are inappropriate for some reason.
End of Introduc7on to Forensic Science Go on to Analysis of Color
Analysis of Color (Bell 11.1, 5-‐5.1)