Everyone’s DNA is slightly different. Thirty-five years ago, when scientists invented a way to distill those differences into a DNA profile, they revolutionized forensic science. That profile—a sort of genetic fingerprint—gave investigators a new and extremely reliable tool for solving crimes.
DNA profiling can be so powerful and has been used successfully in so many cases that some people think it is nearly infallible. But the reliability of DNA profiling varies, and other things being equal, it is most reliable when the evidence contains plenty of DNA from just one or two people. That’s why homicides and sexual assaults—crimes that tend to produce a lot of this type of DNA evidence—made up the bulk of DNA casework for many years.
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