THE STORY OF AMANDA KNOX’S DNA:

If you watch crime dramas, you’ll be forgiven for the impression that DNA evidence makes an airtight case. And if you do have that impression, you might be confused about the internationally famous case of American Amanda Knox, convicted of murdering her British roommate in Perugia, Italy in 2007. After all, the prosecution’s case was based on DNA evidence; Knox’s genetic fingerprints were found by Italian police on the handle of a kitchen knife, which also had the victim’s DNA on the blade.

But not all DNA evidence is created equal — and Knox walked free last week from an Italian jail after scientists savaged the forensic evidence against her as being wholly unreliable. How did DNA analysis go so wrong?

Lots of “scientific evidence” goes wrong.