Use of Search Keys to Solve More Cases with Expanded DNA Profiles

DNA databases have been very effective at developing investigative leads, providing new suspects for unsolved forensic cases.  To date, the majority of forensic laboratories utilize DNA databases with direct matching, where forensic profiles found at crime scenes are compared to profiles from known individuals and must match exactly.  Expanding the size of a law enforcement DNA database can be accomplished by increasing the number and type of qualifying offenses and by including arrestees.  The cost effectiveness of the database size expansion will be examined using a business case, to evaluate the cost benefit of including more known individuals, including the concept of a universal database. The relationship of DNA database size to the number of investigative leads will also be examined.

Indirect matching is a strategy to expand the size of a DNA database scientifically, by utilizing the known sharing of DNA between biologically related individuals.  Currently used techniques include Partial Matching, Familial Searching and Investigative or Forensic Genetic Genealogy (IGG or FGG).  Each of these techniques include indirectly matching the forensic profile to individuals that have not committed the instant crime, but rather are potentially biologically related to the perpetrator.  Indirectly matching candidates are further examined through kinship analysis.  Through building of family trees and comparison of family members to particulars of the crime, suspects are developed for direct comparison to the forensic sample.

A new technique termed Enhanced DNA Indirect Matching (EDIM) will be introduced.  EDIM involves expanding the DNA profile of the forensic samples beyond the core CODIS (Combined DNA Index System) autosomal loci.  This expanded profile permits the strategic use of search keys.  Search keys are areas of DNA which are inherited in known biological and statistical patterns, which enhance the opportunity to locate relatives.  Potentially related candidate profiles are then further evaluated through kinship analysis, to determine whether the candidate is more likely a close or distant relative, or merely a coincidental search key link.

Potential search keys include Y-STRs (Short Tandem Repeats), X-STRs, mtDNA (mitochondrial DNA), and SNPs (Single Nucleotide Polymorphisms).  Expanded DNA profiles permit the development of additional profiles through analysis of these particular DNA regions, or via extraction from a WGS (Whole Genome Sequence) profile.  A case flow for EDIM analysis will be provided to demonstrate and contrast various strategies to maximize the value of forensic evidence, while fitting into current forensic laboratories’ workflows.  Expanded use of UHRs (Unidentified Human Remains) will also be examined as an additional mechanism to resolve outstanding forensic cases.  A business case will be provided to demonstrate the additional crime solving potential of EDIM, using an identical twin extrapolation model to estimate the number of relatives in a DNA database without compromising database security and privacy.  Recommendations for improving the effectiveness of DNA databases, as well as EDIM implementation will be discussed, including bioethical considerations for the various options presented.