There will always be criminal cases, where the evidence DNA sample will not 
match either a suspect's DNA profile, or any in a criminal DNA database. In the 
absence of DNA-based mass intelligence screenings, including familial searching 
(both of which may be restricted by legislation), there is only one option to 
potentially avoid or retrospectively solve "cold cases": the DNA-based 
prediction of human externally visible characteristics of an unknown person 
based on the crime scene sample left behind. Predictive DNA markers are expected 
to be available for some group-specific appearance traits in the near future; 
although it is unlikely that we will soon be able to understand the biological 
complexity of individual-specific appearance. In suspect-less cases reliable 
DNA-based prediction of broader externally visible characteristics from crime 
scene samples are expected to reduce the potential pool of suspects by allowing 
police investigations to concentrate on specific groups of people. Here, we aim 
to describe the forensic motivations for DNA-based prediction of human 
externally visible traits as well as the scientific challenges of finding 
predictive DNA markers, and will discuss examples with promising (e.g. sex, eye 
color and hair color), as well as less promising expectations (e.g. adult body 
height), in the foreseen future. Despite the complex ethical and legal 
implications arising from DNA-based prediction of externally visible 
characteristics, we argue that their use does not lead to a violation of 
privacy. We suggest that likelihood-based results, rather than DNA data itself, 
should be provided to the police for investigative purposes avoiding data 
protection issues. Furthermore, we note that the risk of exacerbating social 
pressure on minority groups due to DNA-based prediction of externally visible 
traits in crime cases may be reduced rather than increased compared to a 
conventional eyewitness testimony. A firm legal basis will need to be 
established for the application of these promising qualitative techniques. To 
gain the attention of legislative bodies, we invite the forensic community to 
participate in a public discourse of these issues.