Blood stains can be crucial in reconstructing crime events. However, no reliable methods
are currently available to establish the age of a blood stain on the crime scene. We show
that determining the fractions of three hemoglobin derivatives in a blood stain at various
ages enables relating these time varying fractions to the age of the blood stain. Application
of light transport theory allows addressing the spectroscopic changes in ageing blood stains
to changes in chemical composition, ie the transition of oxy-hemoglobin into met …