In "Forensics" popular mystery writer Val McDermid outlines the development of modern forensics (scientific analysis of evidence) - a discipline that has literally made it much harder to 'get away with murder'. Rudimentary forensic investigations began long ago: a Chinese coroner's handbook from the 1200s records the story of a murderer caught when flies were attracted to traces of blood on his scythe. Nevertheless, it's likely that many criminals went undiscovered before modern investigative techniques were formulated.
Each section of the book covers a different topic related to criminal investigations such as: the crime scene, fire, insects, pathology, poisons, blood spatter, fingerprints, DNA, bullet markings, and so on. A brief review can't cover the wide array of subjects addressed in the book but I'll give a few examples to provide a 'taste' of the material.
Crime Scene: Modern cameras/photography techniques can record a crime scene in 3-D. Thus experts can determine where a shooter was standing, the trajectory of the bullet(s), how the victim fell, how the blood sprayed, and so on. And the photos can help a jury visualize the crime.
Arson: Additives in accelerants can be used to learn where the fuel was obtained and microbes (diatoms) in the the match heads can be used to trace the matches. One anecdote in this section was distressing: A fire in Ireland's 'Stardust' nightclub in 1981 caused many deaths and injuries because the club owner had locked or blocked most of the fire exits. Arson experts found that the owner didn't start the fire (it was apparently electrical) but he clearly caused the mass carnage. Still, the owner wasn't held legally responsible and even got a big insurance settlement. (I hope Ireland has changed some laws since then.)
Insects: Different kinds of insects attack a dead body in a specific order - so the bug population on a corpse can help determine the time of death. Moreover, the insects consuming the corpse can be ground up and analysed for poisons that were in the body. That's a 'twofer' :)
Pathology: Medical examiners study the body to determine cause of death. Stab wounds can help identify the murder weapon; contaminated body parts can reveal poisons; bullets can point to the gun used; etc. If the knife is sticking out of the victim, of course, that's a huge clue.
Blood spatter: One expert McDermid interviewed noted that she needed to study the entire crime scene in detail to make sense of the blood splatter evidence. She didn't like detectives telling her 'just look at that section of wall beside the victim'... because tiny drops of blood can spray far and wide.
Poisons: Arsenic and other poisons were apparently the murder weapon of choice for royalty (as well as the common folk) for centuries - since there was no way to prove that corpses contained toxins. Once scientists learned how to test for toxins, however, poisoners were regularly caught. Nevertheless it's daunting to think how many people got away with murder over the course of history.
DNA: This is the 'gold standard' of forensic analysis. If someone's DNA is on/in the victim or at the crime scene that person was almost certainly there. This isn't always 100% accurate though, because of human error. McDermid relates an anecdote about a lab tech who used an improperly cleaned tray (someone's saliva was already on it) to analyze DNA...so the spitter was initally accused. Another possible problem here is deliberate contamination of the crime scene by the perp. (Some murder mysteries I've read use this plot device. The perp brings a condom with someone else's sperm and sprinkles it on the victim.)
I was reassured though, when one forensic expert noted that it would be almost impossible for a perp to purposely plant evidence/set up a crime scene to implicate someone else. The analyst noted that the perp would tend to overdo it or do it wrong. For example: leave too much blood; leave the wrong pattern of blood; plant too many glass shards; put evidence in the wrong places; and so on.
At the end of the book I was dismayed to read that attorneys (usually on the defense side) routinely try to intimidate/manipulate expert witnesses to spin things in a certain direction rather than to discover the truth. In some ways vigorous cross-examination is good: One section of the book tells the story of an 'expert witness' physician who insisted that - if several children in a family succumbed to crib death - the parents were definitely murderers. In one afflicted family, crib death turned out to be a genetic predispostion...but the mom, wrongly imprisoned then exonerated, committed suicide. And the 'expert doctor' had his license revoked. Still, I would wish the facts could be brought out without 'politics'.
This is a fascinating book, highly recommended - especially to readers interested in true crime.