Calculating Guilt: Using open-source software in forensic DNA testing

Accepted Session
Short Form
Scheduled: Thursday, June 25, 2015 from 3:45 – 4:30pm in B302/303


DNA testing has become the "gold standard" of forensics, but linking an item of evidence to a person of interest isn't always clear cut. New open source tools allow DNA analysts to give statistical weight to evidentiary profiles that were previously unusable, letting juries weigh the evidence for themselves. This talk will discuss my lab's validation and implementation of the Lab Retriever software package for probabilistic genotyping.


Every DNA match requires a statistical calculation to give it relevance, lest a jury assume that “DNA match” = “guilt”. We must avoid overstating a match— which might lead to a wrongful conviction— but neither can we understate useful data, and let probative evidence go unreported. Our current methods for calculating statistics work well for clean, perfect profiles, but DNA typing protocols are increasingly sensitive, making messy mixtures and partial profiles an everyday challenge. Making use of this data means turning to more complex, probabilistic calculations.

Our lab has been validating the Lab Retriever software package for use in our calculations for the last several months. In this talk, I’ll discuss the sort of data it’s helping with, the issues we’ve had with implementing it (and explaining it to the non-scientists we give our reports to!) and why we chose to use an open source program instead of a popular proprietary software package.


science, legal, government

Speaking experience

I've spoken at numerous forensic conferences, most frequently at the annual meeting of the Mid-Atlantic Association of Forensic Scientists, on case studies, new methodologies, and down-and-dirty research projects. In fifteen years of court testimony, I've had a lot of practice breaking down high-level biochemical concepts for police officers, attorneys, and juries.