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The science behind forensics

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Scientist with petri dish
Scientist with petri dish

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Otzi may have died peacefully, been attacked by one or more people, or animals, or had a tragic accident. Some pieces of evidence fit one or more of these stories better than others. As in real life crime investigation, we will never be absolutely sure of the truth.
Examination of ‘the scene’ where Otzi lay, discovered some weapons, tools, and other bits and pieces.

Alongside fingerprints, DNA is of course, now the technique that most people think of when they think of forensic science. Yet DNA fingerprinting, as the original technique was called, was first used in court in 1988. Current forensic DNA technology, now called DNA profiling, can detect less than 100 picograms of DNA. That is 0.0000000001 grams of DNA. One single cell’s DNA, and you have about 100,000,000,000,000 cells in your body, can be detected.

There’s not much chance that you won’t leave some trace at a scene!
DNA analysis of these and his clothes apparently revealed the DNA of at least four individuals. Some claim that this may show that he was attacked by three people, and the finding of blood on his cloak is thought to suggest that he carried someone on his back.
However, there is nothing to suggest that all of the blood got there during the same incident. Some of these stains could have been made weeks or months before he died. DNA from several animals was found on his weapons. Did this prove that was what he hunted? How else could the DNA have got onto the spears?

You can see how the same observation can be ‘consistent with’ different stories. It is for that reason that the phrase, beloved of crime writers, is not very useful in real crime investigation. It merely means that the story being offered is one of the possibilities. The real job is to evaluate which of the possibilities is the best fit to all of the observations, not just those that fit what you think or wish.

X-rays are a recent development in historical terms and can be used by modern investigators to look at injuries to bones. Even breaks or fractures suffered years before can often be seen by radiographers. They can also sometimes identify victims of accidents or homicide, or sometimes match damage caused by surgery or extraction of teeth to medical records of victims.

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Content last updated: 10/01/2006

 

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