Science Cafe SG is a series of monthly talks on the last Thursday of every month on topics of scientific enquiry. Follow them on Facebook.
The CSI effect
Forensic science has been popularised by the Hollywood series, CSI – Crime Scene Investigation since its debut in October 2000. After more than a decade, the interest in forensic sciences is still mounting, prompting numerous tertiary institutions to run forensic science programmes, with the National University of Singapore (NUS) having one such module.
Dr Ng Ngan Kee from the Department of Biological Sciences, NUS was invited to speak on the topic in a talk organised by Science Cafe SG at the Earshot Cafe.
Dr Ng said that the reality of CSI versus forensic science couldn’t be further from the truth; cases are not always solved quickly as depicted! How would you expect to solve a case in a few days?!
The crime scene
Forensic science is the application to investigate situations after the fact, and to establish what happened based on collective evidence. The concept is based on Edmond Locard’s Exchange Principle, which was the “perpetrator of a crime will bring something into the crime scene and leave something from it, and that both can be used as forensic evidence”.
The police or crime scene is preserved so that the forensic scientists can collect such evidence, though often hampered by other conditions such as rain or wind. At the crime scene, numbers are used to denote evidence, and alphabets for bloodstains. Based on the evidence, the forensic scientists will reconstruct a crime scene, to be used in court to prosecute.
In Singapore, most of the analysis is done by forensic scientists at the Health Sciences Authority, and often the scientists are accredited every few years to maintain relevant skills.
1) Human fingerprints
- Fingerprints are the most common evidence looked for in crime scenes. Human fingerprints are formed in the embryonic state, and unique to each individual, even for identical twins.
- Fingerprints are not unique to humans, as certain animals such as koalas have unique fingerprints.
- The Automated Fingerprint Identification System (AFIS) was developed by the Federal Bureau of Investigation.
- Eyewitness accounts are often unreliable, due to lookalikes, and the emotional conditions of the eyewitness at that point of time.
- Latent prints can be gathered by (1) dusting, or (2) superglue fuming.
2) Blood samples
- Bloodstain Pattern Analysis (BPA) interprets bloodstains at a crime scene to recreate the actions that caused the blood splatter. Analysts examine the size, shape, distribution, and location of bloodstains.
- There are methods to tell human versus animal blood.
- There are always residues left behind though the crime scene is cleaned up. These include luminol, flourecein, hemascein, and blustar.
3) Forensic Biology: DNA Analysis
- A drop of blood is enough to extract DNA.
- DNA analysis can take several days as you need to extract the DNA from the cells and amplify the DNA.
- Blood, hair (must be from the root), tissue, body fluids, and skin are among the sources of extracting DNA. It helps with the identifications of victims, perpetrators and victims of mass disasters.
- Fibers from the carpet, strings, clothes are also often used as evidence – composition of fibers are unique.
- Wounds and weapons are not always perfect due to the elasticity of human muscle.
- Firearms can be used, looking at scratches, striation marks) left on bullets by the barrel of a pistol or rifle. Gunpowder residue.
- Tool marks can leave striation and other marks of surfaces. These marks can be compared to the tool believed to have made them.
5) Trace evidence
- Footwear analysis can be very distinct.
- Tire track analysis that matches to tire impressions, thread width.
6) Other evidence or cool shit
- Handwriting analysis: Spaces between letters, words, lines; placement of words on a line; margins left empty on a page.
- Forensic entomology: Determining the length of death via insects.
- Forensic odontology: Matching via teeth bites.
- Paint analysis: Particularly useful for car accidents.
- Forensic pathology: To determine the cause of death.
- Forensic toxicology: Testing substances in powders, pills, liquids, bodily fluids.
- Forensic athropology: Identification from bones (gender, race, facial reconstruction).
- Forensic botany: Using plants, pollens, algaue to differentiate the possible murder site and crime scene.
These methods are not just used to solve crimes, but also in mass disasters. A combination of different methods are used to identify the victims.
About the Speaker:
Ng Ngan Kee is currently an Instructor in the Department of Biological Sciences, National University of Singapore. She has been involved with the Minor in Forensic Science programme in NUS since its inception in 2008. She is also teaching one of the essential modules required in the minor programme.