Scientists have created a new test to help the police catch criminals.
The Hirisplex system can tell the police what colour eyes and hair a criminal has by using DNA left at the crime scene.
The test is effective on even small samples of DNA which scientists can take from things like someone's blood or skin.
The new system will help to narrow down suspects and help the police find out who committed the crime.
On average, the accuracy was 69.5% for blonde hair, 78.5% for brown, 80% for red and 87.5% for black hair colour.
Professor Kayser who led the study said: "The test is very sensitive and produces complete results on even smaller DNA amounts than usually used for forensic DNA profiling."
This type of technology is useful in a situation where the police have no idea who might have committed the crime, for example if there were no witnesses.