Opinion ID: 1979318
Heading Depth: 1
Heading Rank: 3

Heading: The DNA Samples in this Case

Text: Samples were cut from several places in the crotch of the underwear worn by the child, K.W., at the time of the assault. Semen was extracted from some of those cuttings, and the semen samples were processed to separate sperm from other substances. Because too little DNA was extracted from the resultant three sperm samples, they were combined before being amplified and run through the PCR/STR automated typing instrument, and were labeled Q1-3/4/6M. The corresponding non-sperm samples (Q1-3F, Q1-4F, and Q1-6F) were processed individually. The four resulting DNA samples were first analyzed using the Profiler kit, which tests nine of the thirteen CODIS loci, plus the amelogenin site, which tests the sex of the DNA contributor(s). The results of the Profiler test showed that all four samples were unresolvable mixed samples, meaning that while each contained alleles from more than one contributor, the alleles could not be reliably divided into individual pairs corresponding to each contributor's unique DNA profile. [5] Samples Q1-3F and Q1-3/4/6M contained male and female DNA; the other two contained only female DNA. Only the Q1-3F sample was tested at additional loci using Cofiler, because the Q1-3/4/6M sample did not have enough DNA left after the Profiler test to test using Cofiler. The Cofiler test identified an additional four loci in the Q1-3F sample. According to Dr. Baechtel, all of appellant's and K.W.'s alleles could be seen in the alleles found at the thirteen loci in the Q1-3F sample. Thus, he concluded that both appellant and K.W. were possible contributors to the mixed DNA in that sample. The alleles found at the nine Profiler loci examined in the Q1-3/4/6M sample also were compared to the alleles found at the same nine loci in appellant's and K.W.'s known DNA samples. All of the alleles possessed by appellant and K.W. were consistent with the alleles present in the Q1-3/4/6M sample, so Dr. Baechtel also concluded that appellant and K.W. were possible contributors to that mixed sample. After he concluded that neither appellant nor K.W. could be excluded as possible contributors to those samples, Dr. Baechtel calculated a match probability statistic that estimated (in his words) how likely it is to go out into the general population and find someone who has a DNA profile such that they could have contributed to that [DNA evidence sample]. The statistic he reported was based on sample Q1-3F, which was the most informative because it contained thirteen loci as opposed to only nine loci in the Q1-3/4/6M sample. The resulting estimates of the probability of a random match were approximately 1 in 410,000 African-Americans; 1 in 5.5 million Caucasians; 1 in 3.5 million for Southeastern Hispanics; and 1 in 8.5 million for Southwestern Hispanics.