How forensic scientists gather vital evidence to solve crimes

August 30, 2026

AI Summary

5 min read

In 17th and 18th century courtrooms, a case without a weapon or an eyewitness was mostly "he said, she said." Witnesses could be bought or biased. The need for a neutral, repeatable way to link a person to a crime scene is what gave rise to modern forensic science. As science journalist Sanjuncta Mondol explains in this episode of Instant Genius, the field has evolved from crude village tests to molecular-level precision—but it still depends heavily on human interpretation and context, a fact that TV crime shows routinely ignore.

From rice-in-the-mouth tests to fingerprint classification

Before modern forensics, societies improvised. Mondol describes an old Indian method for identifying a thief: village elders would gather all suspects and ask each to hold a handful of rice in their mouth. The logic was that a nervous liar would produce less saliva, so the person whose rice came out dry was considered guilty. It was deduction, not science, but it addressed the same problem forensic science tackles today: how to find the truth when no one saw what happened.

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What you'll learn

1 (03:04) **Defining Forensic Science** - The guest explains the etymology and modern definition of forensic science.
2 (03:46) **Early History & Pre-Scientific Methods** - A look at how crimes were solved before modern forensics, including ancient Chinese and Indian techniques.
3 (06:05) **The Science of Fingerprinting** - The origin of fingerprinting with Sir Francis Galton and the Henry Classification System.
4 (09:19) **How Crime Scenes Are Swept for Prints** - Explaining Locard’s Exchange Principle and the practical techniques for finding fingerprints.
5 (11:39) **The Myth of the Instant Fingerprint Match** - Why TV shows mislead viewers about how quickly and easily prints are identified.
6 (14:31) **Sources of DNA at Crime Scenes** - The many ways humans shed DNA and the challenge of context.
7 (16:52) **The Danger of Cognitive Bias in Forensics** - A real-world example of a forensic analyst who manipulated results.

+ Full timestamped outline available in the app

Show Notes

Whenever a crime is committed, tiny traces of evidence are left behind at the scene, which, if pieced together correctly, can tell us exactly what happened, when it happened and who was responsible. This is the job of forensic scientists. But how exactly does this process work, how accurate are the portrayals of crime scene investigators we see on film and TV, and what happens if when mistakes are made?

In this episode we’re joined by science journalist and author Sanjukta Mondal, to talk about her latest book, Forensic Science.

She talks through the fascinating history of forensic science, explains how we all leave traces of our presence wherever we go, and tells us about some of the common myths and cliches we often see in TV crime shows.

Take your curiosity further with a subscription to BBC Science Focus magazine. Every issue is packed with fascinating insights into the science behind everyday life, the latest breakthroughs and expert analysis, delivered straight to your door. Receive an extra £5 when you subscribe using the code SF5OFF, (minimum spend £20, see full terms and conditions on our website).

https://www.ourmediashop.com/bbc-science-focus-magazine-pod30

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