Processing the Backlog of Sexual Assault Evidence From a Brazilian Forensic Genetics Laboratory Using Automation

The accumulation of untested sexual evidence is a common problem for many forensic laboratories. In Brazil, there are around 150 thousand sexual evidences awaiting DNA processing. At the same time, manual extraction by differential lysis of these evidences is laborious and time-consuming. In this regard, the Brazilian federal government has structured and sponsored forensic genetics laboratories, providing automated platforms for evidence processing, with the objective of clearing the backlogs of sexual evidence and feeding the national DNA database. This study aims to evaluate the results from processing the backlog of sexual evidence in the forensic genetics laboratory of the Instituto-Geral de Perícias do Rio Grande do Sul to verify if the use of automation is an efficient strategy to manage large amounts of stored evidence. A total of 614 cases of sexual assault (1026 sexual evidence) from the last 10 years (2013 to 2023) with at least one sample with positive results for spermatozoa detection were analyzed. Samples were submitted for DNA extraction by differential lysis on the Hamilton Microlab Autolys STAR SAE platform, followed by the amplification of STR autosomal markers, capillary electrophoresis analysis in the ABI 3500 genetic analyzer and insertion in the BPG-RS using CODIS 7 software. The cases were stratified into three groups, according to the year in which they occurred (182 cases from 2013 to 2016; 123 cases from 2017 to 2019 and 151 cases from 2020 to 2023), in order to verify whether there were differences in the efficiency of differential extraction due to the storage time. 374 cases (61%) presented at least one sample with an eligible autosomal genetic profile for DNA national database. In 64 cases (10.4%) it was possible to obtain only the Y chromosome haplotype profile. From each sexual assault case, only one sample was inserted in the DNA national database. Cases from the years 2020 to 2023 presented 68% of autosomal eligible profiles, followed by cases from 2017 to 2019 (58%) and by cases from 2013 to 2016 (54.9%). The results of this study support the importance of processing the backlog of sexual samples as soon as possible in order to get more eligible autosomal profiles for CODIS (p < 0.05). Using automation to reduce the size of the backlog has been effective, allowing the simultaneous processing of a large number of samples, with reliability and less chance of contamination.