  Homicide investigations often depend on the determination of a minimum
post-mortem interval (PMI$_{min}$) by forensic entomologists. The age of the
most developed insect larvae (mostly blow fly larvae) gives reasonably reliable
information about the minimum time a person has been dead. Methods such as
isomegalen diagrams or ADH calculations can have problems in their reliability,
so we established in this study a new growth model to calculate the larval age
of \textit{Lucilia sericata} (Meigen 1826). This is based on the actual
non-linear development of the blow fly and is designed to include
uncertainties, e.g. for temperature values from the crime scene. We used
published data for the development of \textit{L. sericata} to estimate
non-linear functions describing the temperature dependent behavior of each
developmental state. For the new model it is most important to determine the
progress within one developmental state as correctly as possible since this
affects the accuracy of the PMI estimation by up to 75%. We found that PMI
calculations based on one mean temperature value differ by up to 65% from PMIs
based on an 12-hourly time temperature profile. Differences of 2\degree C in
the estimation of the crime scene temperature result in a deviation in PMI
calculation of 15 - 30%.
