This is a really good question! A forensic scientist would be able to tell you more about this but the simple answer is that every person has a unique fingerprint – no two people are the same! Even though they may look similar to the naked eye, under a powerful microscope every fingerprint presents a slightly different picture and that’s how police can tell two people apart. There are lots of different classification systems for fingerprints that I expect the police would use to help them. It’s all computerised these days so I’m sure that makes their jobs a lot quicker!