Session

STRmix & CODIS: LAPD Software Solutions

Tuesday September 15th, 2020 // 12:19 pm - 12:43 pm

With the increasing adoption of probabilistic genotyping software for forensic DNA mixture analysis, the need for methods to upload and perform comparisons for deconvolutions has risen. LAPD has developed internal solutions and methods to develop profiles suitable for CODIS upload from STRmix deconvolution results as well as software tools to aid analysts in comparing possible candidate matches to evidence samples. This presentation will demonstrate how LAPD uses excel-based programs to handle STRmix deconvolutions for sample to sample comparisons, generating CODIS eligible profiles, and resolving large numbers of database hits.

 

STRmix deconvolutions generally are a list of probable genotype sets that can explain a given evidence profile organized by weight. Though the genotype sets are fantastic for considering possible genotypes, it can be difficult to determine how best to generate a CODIS eligible profile from them. LAPD has developed an excel-based program named POPSTR (Probability Optimized Profile) that imports STRmix results files and generates full or partial single source profiles whenever possible. This presentation will walk through how POPSTR generates a single source profile from STRmix deconvolutions, evaluates which genotypes or alleles to use based on weights, automatically calculates MME/MRE for CODIS eligibility, and how the software can switch over to generating mixtures when single source profiles cannot be developed.

 

It can be difficult to determine which sample is best to upload into CODIS for cases with multiple mixture samples, especially when they contain a common contributor. The STRmix deconvolutions for each sample are often different even with a shared contributor and it’s not always obvious where the contributors can line up. Through the FORESTR software, LAPD is able to compare multiple samples and contributors in an easy to read side-by-side view that aids analysts in making an informed choice. This talk will cover how FORESTR is used by LAPD DNA analysts to compare multiple mixture samples and find which sample and which contributor is best used for CODIS upload.

 

Finally, this presentation will go over the DATABSR program that was created by LAPD in order to rapidly evaluate CODIS hits. LAPD averages around 150 CODIS hits a month and required a tool to help resolve the hits in a timely manner. DATABSR is able to automatically pull the STRmix result files that generated CODIS hits, calculate likelihood ratios for the potential candidates, and create a report of all matches with LRs above a set threshold. This talk will cover how DATABSR works and is utilized by LAPD’s CODIS team.

Speakers

Brian Kim

Criminalist, Los Angeles Police Department

Brian joined LAPD in 2011 and was assigned to the Serology DNA Unit which processes over 20,000 DNA samples a year. He is currently a member of the validation team which evaluates and implements new technology to assist in forensic DNA analysis.

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