kyriacos writes: Dutch forensic experts discovered how to accurately date fingerprints, a breakthrough that could one day let police date crime scene prints from years ago. Fingerprints leave nearly-unique marks on a surface that can be copied and compared to a database to identify a suspect, a police technique that rose to prominence in the early 1900s. The prints themselves are made up of sweat and grease, including a complex mix of cholesterol, amino acids and proteins. 'The chemicals in these fingerprints can be analysed,' said Marcel de Puit, fingerprint researcher at the Dutch Forensic Institute (NFI). 'Some disappear over time and it's the relative proportions of these chemicals that allow us to date a fingerprint.' As the database expands, so should the technique's reliability, allowing police to date fingerprints from several years before.