Writing in Analytical Chemistry , Paige Hinners and Young Jin Lee of Iowa State University say they have figured out an accurate way to data to within 24 hours when a fingerprint under a week old was made -- and thus whether it is associated with a crime temporally, as well as spatially. The Economist reports: They knew from work conducted by other laboratories that the triglyceride oils contained in fingerprints change by oxidation over the course of time. That provides an obvious way to date prints. The problem is that the techniques which have been applied to analyze these oils are able to distinguish age only crudely. In practice, they can determine whether or not a print is over a week old, but nothing else. Dr Hinners and Dr Lee wondered if higher precision could be obtained by thinking a bit more about oxidation. Oxygen molecules in the air come in two varieties. Most have a pair of atoms but some, known as ozone, have three. Though far rarer than diatomic oxygen, ozone is more...