Apparently the heritability of blood types was known since 1910 https://en.wikipedia.org/wiki/Blood_type#History https://en.wikipedia.org/wiki/Blood_type#Histo

Apparently the heritability of blood types was known since 1910 https://en.wikipedia.org/wiki/Blood_type#History https://en.wikipedia.org/wiki/Blood_type#History and some information about blood typing was famous enough to get the medicine Nobel in 1930 https://en.wikipedia.org/wiki/Blood_transfusion#20th_century https://en.wikipedia.org/wiki/Blood_transfusion#20th_century So maybe you could try to draw an analogy and say "as with blood typing, many more hereditary structures and features of tissues will be discovered at the chemical and microscopic levels, collectively sufficient to perform definitive studies of hereditary relationships on the basis of tissue samples". It might be credible at that level, even though that description is a little bit misleading (because you're not actually using random sets of phenotypic features, but rather the actual underlying genetic data). But I imagine the coroner could at least believe that there are microscopic features that are heritable that would one day be subject to more and more informative analysis. And blood types could be a good prototype of that. I'm not sure the coroner would find it that intuitive that genetic information is carried or expressed in hair, though!