Fingerprints can now be dated to within a day of when they were made

SINCE THE first use of fingerprints to identify and convict a murderer, in 1892, detectives the world over have come to rely heavily on print evidence to build their cases against suspects. One limit on the value of fingerprints, though, is that it is hard to work out how old they are. This is a particular problem when a crime is committed somewhere that a suspect frequently and legitimately visits, such as a place of work. In this case exactly when a print was made might be crucial to establishing guilt or innocence. But it is information that science has, until now, been unable to provide with any accuracy.

As they write in Analytical Chemistry, Paige Hinners and Young Jin Lee of Iowa State University believe they can remedy this state of affairs. 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 analyse 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.