Constance Fisher

Preliminary Hearing

October 29-30, 2003

Summary
The hair found in Scott's pliers is important to the prosecution to link Laci to Scott's boat. Fisher explained the difference between mitochondrial DNA and nuclear DNA. FBI analysts compared the hair found to one of his blood samples and to DNA on a test swab designated as "SR2," obviously from Sharon Rocha, as mitochondrial DNA is passed from maternal relatives. According to Fisher, the hair did not match Scott's blood sample, but did match the SR2 sample. Because everyone in a maternal line carries the same mitochondrial DNA, it cannot be used as an unique identifier. 1 in every 112 Caucasians would be expected to have the same DNA sequence, as would 1 in every 159 Hispanics. Mark Geragos challenged Fisher’s qualifications. Under questioning, Fisher acknowledged that she had never testified in California state court and that this was the first case where she was testifying about the admissibility of mitochondrial DNA evidence. 

October 30, 2003

Summary

Thursday's hearing was filled with excruciating detail on mitochondrial DNA analysis, as Geragos grilled FBI expert Constance L. Fisher. FBI lab technicians had one of Laci Peterson's bones but did not extract DNA from it to compare with DNA from the hair found in Scott's boat. Geragos tried to get Fisher to say that reliability of such tests is the subject of much debate in the scientific community. "There is always debate going on in a community," Fisher said. But, she said, disputes about mitochondrial DNA are not "sizeable." She conceded that she had not visited six of seven laboratories that contributed tissues to establish a database used by the FBI. Geragos also took aim at the computer program used to analyze the DNA data.  Fisher said the program, written by a former lab employee no longer with the FBI, had some built in error but that analysts checked the results manually. "Was he fired for incompetence?" Geragos asked. Fisher said he left to study law, prompting the packed courtroom to erupt in laughter. Scott chuckled with nearly everyone else, then briefly shook his head from side to side as he smiled.