Police investigators today begin searches for perpetrators with conventional DNA profiling – comparing a genetic signature from sperm or hair left at a crime scene with a database of identified offenders. But that doesn’t finger culprits who have never been registered. A growing technology called ‘DNA phenotyping’ is now aimed at interpreting genomic clues about a suspect’s possible external appearance. The science behind it is new, and investigators have to navigate the statistical uncertainties – as well as ethical and legal questions – the technology is raising all over Europe.