Using the Swiss national DNA database (NDNAD) as an example, this paper reports on research undertaken to establish scientific foundations that pertain to the use of partial SGM Plus loci profiles for investigations.
The study concludes that searching NDNAD with DNA profiles with less than a suggested number of loci for a match (e.g., less than six) can potentially aid an investigation. The study found that comparing 10,000 simulated partial DNA profiles with only 4 loci with a simulated NDNAD of 100,000 persons returned at most 3 persons as possible candidates for 80 percent of the profiles (if the trace from the perpetrator was included in the search). Giving a list of three people to the police for investigative purposes would be useful. The effect of the size of the database was examined for sizes of 100,000 and 200,000 persons. As expected, the number of matches with partial DNA profiles depends on the size of the database; however, the parameters of the investigation based on existing evidence and locality are likely to enable a reduction in the size of the suspect population. The research reported in this paper allows collecting information on the range of the number of matches observed in the simulations. This may inform guidelines that can help in deciding if it is appropriate to search the database according to the expected number of candidates, the circumstances, and other information about the case. A pilot study could ensure that results in actual cases are similar to the simulations reported in this paper. In pursuing this course in an investigation, investigators should understand the difference between using partial DNA profiles to limit the pool of suspects and the use of standard DNA profiles as evidence for an arrest. 7 figures, 4 tables, and 13 references